When I 1st encountered a werebeast as a player in 5e, I wanted to know everything since I've always loved werewolves. When I first read the Lycanthrope section in the 5e MM I was disappointed with how basic it was and that the immunities are all the same. I then browsed Curse of Strahd and Van Richten's Guide to Ravenloft hoping for more depth and lore and was further disappointed.
Recently a DM friend of mine prepping for Curse of Strahd shared with me his copy of AD&D 2e Van Richten's Guide to Werebeasts and I read the whole thing. While all are still vulnerable to magic weapons, each werebeast species has its own non-magical weakness (eg. obsidian weapons & ginseng for weretigers, copper weapons and fennel for werejackel). Additionally there are details & traits about being born vs being infected, heritability, social life, diet, lairs, morals, etc. I then checked the 2e MM and there is a lot more detail for each werebeast than the 5e MM.

Why aren't werebeasts as developed in 5e and where is the lore to go with them? I would love to see an updated guide to werebeasts in One D&D.

Its all much more generalised and streamlined.

D&D has become less about setting the story and lore of things and more about setting the rules and base framework, even in adventure books.

The idea is that the DM (and players to an extent) should expand and extrapolate the storyline and scenes with their own creativity and roleplay, encouraging homebrew and customisation.  Unfortunately, many players are also fans of the general fantasy reading genre and enjoyed the DND content for it's own lore and creativity in the older editions.

And this is why the deep library of lore from older editions is a great tool for DMs running games in 5e.

Bluntly, if you like those rules, use them.

I adore werewolves, but they and other lycanthropes are victims and doomed in my current setting and next one.  Went back to the universal style beasties for them.

if you are not the DM, ask. If you are, the thing is add them in and enjoy it.