Was the removal of nonmagical BPS res and immunity a good descion?

So one of the biggest changes to monsters in 5.5e has been the removal of resistance or immunity to bludgeoning, piercing, and slashing damage from nonmagical attacks. 

The replacement was either buffing monsters who had it in other ways (like more HP or higher AC) or by making the resistance universal to magical weapons as well, and removing flat immunity to BPS. Was this change justified and a good desicion?

In practice, resistance to non-magical BPS was a non-issue in actual play.  By the time those sets of abilities proliferated drastically every single player was likely to have at least a +1 weapon (which is just an uncommon, non-attuned item, after all).  That meant there were wasted words on a statblock that did not really influence gameplay, which is a strong sign something should not be there.  Additionally, this was a minor annoyance and barrier to entry or new players, who might get bogged down on the distinction between non-magical, as well as a potential trip-up for experienced players who are so used to instinctively seeing these abilities as "nonmagical" they might instinctively read a non-existent "nonmagical" into a stat block when, in fact, it is supposed to be true resistance to those damage types.

Now, instead of a useless signal taking up space and informing the DM nothing of value, the signal is used when it actually matters, making sure this information is only provided when it is going to have a real influence on the game. 

If you really want monsters that can only be defeated in a special way, regeneration or other special death mechanics generally do a better job than immunity. I've used werewolves with regeneration 5 (prevented by silver), and it forced PCs to actually seek out a silver weapon, rather than relying on PCs who did non-physical damage.

I'm fine with the removal of immunity to nonmagical damage, especially given that 5E had already changed Magic Resistance so it was no longer a flat percentage chance of spells simply not working on the target.  A mechanic that just shuts down a class or worse, group of classes, is just adding an element of anti-fun for some of the players.

Narratively the concept had benefit since it helps explain why high-tier threats that should hold the attention of a kingdom/empire/major organization/etc. need to be resolved by a small group of adventurers rather than deploying an army of conventional forces. As noted here, though, it was such a nominal gate in a lot of campaigns that it turned into page clutter, and otherwise often represented a stumbling block for the inexperienced on either end if they were unaware of it or failed to appreciate its effect on combat.

Quote from The_Ace_of_Rogues >>

Narratively the concept had benefit since it helps explain why high-tier threats that should hold the attention of a kingdom/empire/major organization/etc. need to be resolved by a small group of adventurers rather than deploying an army of conventional forces.

I give monsters like that a modified damage threshold (modified in that a character with multiple attacks can add them together to determine whether the threshold is exceeded). A damage threshold of 10 is mostly immune to the village militia but will be consistently blown through by tier 2 characters, a threshold of 20 is essentially immune to mooks.

I agree that the removal from most monsters was a good descion. It was so demoralizing to players who didn't have magical weapons realizing that all their attacks would do half-damage, especially since so many monsters in 5e had it.

My only gripe is that some monsters like incorporeal undead kind of suffer from its loss, because since BPS immunity doesn't really exist, it removes some flavor.

Quote from PPSS2022 >>

My only gripe is that some monsters like incorporeal undead kind of suffer from its loss, because since BPS immunity doesn't really exist, it removes some flavor.

 Well, they weren't immune in 2014 either. Just resistant, and now they're generally resistant to BPS.

I meant immunity that can be overcome by magic BPS.

I didn’t love it when it was a thing, but I don’t think the solution of just make them resistant to all bps is better. 
In the old way, as others said, it rarely came up. There was a window between level 3-5 where it could matter, but after that pretty much everyone had a magic weapon. There is something to be said about it, in terms of world building as it made a good reason why the average town guardsman would be extra scared of those kinds of monsters. But for the PCs, it rarely came up. 

However, the current way of just resisting bps, magic or not, just seems like a big “screw you” to martials, while the wizard is happily fire bolting with no problems.

Quote from Xalthu >>

However, the current way of just resisting bps, magic or not, just seems like a big “screw you” to martials, while the wizard is happily fire bolting with no problems.

Incorporeal creatures with resistance to BPS are also resistant to fire. Mostly what it does is put a high value on radiant, force, or psychic damage.