Why did they remove regen from vampires?

Like, I know that they still regain HP from biting people, which is nice, but I'm still a little disappointed that flat regen got removed from ALL vampires. For vampire spawn it makes sense gameplay-wise. (Running regen that can be disabled for a lot of monsters is a DM nightmare). But for full vampires it's just a little disappointing. (The lore of vampire's regenerating is that they kind of heal instantly if they HAVE drank blood recently, not only if they directly drink it). What do you think?

There were game design issues where Regeneration could make a fight way too easy or way to hard depending on how much damage the party can deal each round. Nixing Regeneration helps ensure more consistent difficulty.

Quote from Maruntoryx >>

There were game design issues where Regeneration could make a fight way too easy or way to hard depending on how much damage the party can deal each round. Nixing Regeneration helps ensure more consistent difficulty.

I don't know. Trolls and Revenants still had regen tho, so clearly it wasn't bad for all monsters.

Yeah, but regen is basically the defining trait of trolls.  Also, trolls don't have an special movement options.  Vampires are hyper-mobile.  With regen they can easily rush in, do some damage, then escape only to come back a minute later after getting back up to full health and hit the party again.  And again.  And again.  I've been on the receiving end of this sort of tactic before and it's pretty much the opposite of fun.