You know, random side tangent here actually:
So the original Resident Evil is mostly content just doing the zombie thing, and the big reveal, such as it is, is hey there's a whole evil corporation making zombies on purpose oh no they can unleash zombie plagues anywhere they want in the world.
RE2 starts from the already much bigger point of "oh whoops, the whole city is crawling with zombies, damn, but we still need a big reveal, so we have this whole G-virus plot, and we're really honestly doing an excellent job of selling "oh, yeah, the zombie virus we already had was pretty bad because it turns everyone into zombies, but at least zombies aren't actually all that threatening, you can just shoot'em or whatever and lock all your doors with chess piece locks they can't solve. This new virus though, wow, this is a problem, because anyone exposed to THIS one turns into this ever-mutating horror that's a huge unstoppable force with increasingly weird powers, like Zeiram or something. So yeah it's imperitive that nobody ever gets to use THIS for real.
... and every game past there just kinda has had whatever big bad final boss-y type (or even just regular stuff) also do this wild mutation come back if there's even a couple still living cells shtick, without any justification for it at all. It's most egregious in 3 because that one's set more or less concurrently with 2, so it's like "we need black ops teams everywhere looking for our one researcher with the big blobby monster virus! That's invaluable to our cartoon villain plans! Also we should deal with those nosy cops with our new super monster agent." "Oh, is that something you made with early samples of this virus you're after?" "No, we kinda just took a regular tyrant and gave it a speak and spell? It was slow glowing but look he can wear a little coat and fire a rocket launcher and talk, kinda!"
So by 2 remake it's just like... oh this is just some zombie guy. They all do this.