Their must be hundreds if not thousands of adventure modules created why can't they just be updated to 5e? I'm looking at my sources and I have 33?  Like take my money already update the old adventures it has to be cheaper then making them new?

The only thing they'd be able to keep is the storylines neband maps, everything else would have to be redone to match 5e balancing. Their savings would be marginal over producing a new adventure. The only people it would have a different appeal to over a new adventure are the older players with nostalgia, who probably have the old version...and many would probably prefer to do their own conversion, reducing the demand compared to a new adventure. People exist who would buy it...but it's generally probably more profitable to pay for a new story than to recycle old ones with a small target customer base.

It does make sense to have lots of smaller adventures recycled so the nostalgia pull is wider. That's what we're seeing, though - compendium adventures like Ghosts of Saltmarsh and Tales from the Yawning Portal recycling stories from previous editions.

Maybe they'll recycle a full adventure, but I'd imagine that they'd continue to rather to invest in new ones than old ones.

Go to DMsGuild and look for Classic Modules Today. They’ve converted a lot of old things to 5e and they are only a few bucks each. I use them all the time.

so, the answer is apparently, everywhere but here.

Perhaps some specific nes you are interested in?

Aerie of the Slave Lords (a1 to A5) would be a good one for them to redo.

I liked the early C series -- and Ghost Tower has always been localized to my campaigns since it came out.

The GDQ series has kinda been played around with concept wise, but the could do the full GDQ set up (Giants, Drow, and then Lolth) but they would spend a LOT of time fixing it.

I always liked the I series, especially The Deserts of Desolation stuff (I-3 to 5), but also I-11 and I-12.

They can't do Mystara, hyborian Age, Lankhmar though -- no longer have the license for Mystara or the others. That wipes out about half of all the modules previously published (seriously) for 1e and 2e. THey were based in Mystara and balancing out the conversion stuff would mean essentially rejiggering FR and, well, based just on this forum, I wouldn't think they would dare, lol. Arneson took back the rights to Mystara, and that means they have to essentially completely rewrite the modules -- and FR doesn't have a space for Hollow Earth or some of the John Carter or Carson  stuff that Arneson set up in those games.

All of the Top Ten of All Time are currently available in updated versions for 5e -- see the suggestions above.

But note that I am looking at 1e and 2e to start, here. 3e through 4e are sometimes still available, and many of them were adapted for pathfinder rules.

Wizards absolutely owns the rights to Mystara, they just choose not to use it. Arneson had zero to do with it. He was long out of the picture before it came along, though there was an attempt to incorporate some of the Blackmoor background into the setting at some point.

The main issue with adapting Basic, 1e or 2e modules is that direct conversion is all but impossible. The power levels of characters and the style of play they were written for is significantly different than modern D&D. Its just not worth it for Wizards to invest the money into that vs writing new material, or the adaptations that are loosely based on them as they've done a few times. If you want to run the old stuff, as already suggested, the Goodman OAR books, or the CMT conversion documents are the way to go. 

I've dabbled in "serious" conversions of 2e to 5e and it takes a lot more time to get it right than it does making something not bound to an original text.  It actually reminds me of translation work, which is more labor-intensive than someone saying "just make it so" may realize.

I usually just convert the older stuff myself for my own use. It isn’t that hard.

I could be wrong, but I would think a few conversion people have to be cheaper than a whole new creative endeavor with an Author.

Quote from MidnightPlat >>

I've dabbled in "serious" conversions of 2e to 5e and it takes a lot more time to get it right than it does making something not bound to an original text.  It actually reminds me of translation work, which is more labor-intensive than someone saying "just make it so" may realize.

 So, you find the whole creative process of the story line NPC's encounters etc. easier to recreate then changing what the dice do?

Update: I found a source for the old content

 https://archive.org/search?query=subject:"DUNGEONS AND DRAGONS"

Quote from AngryGamers >>

I could be wrong, but I would think a few conversion people have to be cheaper than a whole new creative endeavor with an Author.

 Cheaper. It's not that much cheaper though. The hard work isn't really so much in writing a story so much as balancing encounters, making sure that they match the theme etc. I can whack out the story in an evening. A couple more to flesh it out, tweak it, and so forth. The real cost is making the encounters that are not only thematically appropriate, but also difficulty appropriate and  provide the right tone. That's all got to be done again. Yes, you are saving some money by taking the old stories...but you're also narrowing your consumer base because the people most likely to be interested...already have it and are the most confident in doing their own conversions. So pay a bit more, and you can have an adventure that everyone is open to and you can direct it to the tastes of the 5e consumer base (which, as many hangers-on of old editions frequently remind us, is not the same as the old editions).

It can make sense if your business model is to serve that niche. People come to your site because they're specifically looking for those conversions. But when you're WotC and can make plenty of money just putting out new, more profitable content? Makes more sense to spend that money investing in new adventures, for the most part. It's a tad more expensive...but you get more money in return. They generally need a reputable publisher to succeed (old edition adventures can sell on their reputation, new adventures don't), but WotC has that reputation. At least, big enough to sell new adventures.

It's not just about how cheap it is to produce, it's about profit, and that depends how many you can sell. New adventures have higher potential.

I like a lot of the Baldman Games materials on DMs Guild. Pretty good about maintaining internal consistency and enough out there to do a whole campaign from 1st-20th level.

Back in 2017  someone somewhere had a PDF that had Conversion rule son it for PC's NPC's and adventure for all previous versions of DnD  through 4e...

It was called "DnD Conversions" simply enough...

May still be out there somewhere  If I can find the copy I had I will post here

DnD Conversion PDF

I think this is something that WotC should have been doing from the day 5E came out.

They had a hundred stories already written and basically just needed to change a few things in each module. The excuse of balancing encounters is a weak one. For one it would have shown them the problems they had with the CR system they adopted and the changes to the monsters.

They owned all the artwork and maps already so no cost there.

We are talking a conversion taking at best 2 months vs paying an author/dm to come up with a whole new module for a year or more of work. With a good group of people they could have had a dozen out in a year. They could have even stored them up for a new release every 6 months. 10 years of modules all shelved up and ready to go.

How many new players and younger players have even played the old modules? Not many at all, they would be all new to a huge amount of players.

Plus they could have cut off all those 3rd party people who did cash in on the idea. Then instead of charging them some royalty fee they would have gotten all the cash.

my understanding is that Wizards *did* have an agreement with folks to produce conversions for existing modules. Directions to several of them were earlier.

But a conversion is not exactly a whole new book to sell. Or to buy for a new DM.