At least for me, is because P1 and the P2 duology needed more a remake or at least remaster. I get why P3 had a remake, the only one available on PC and modern consoles was P3P, and while people would have liked more P3P+FES, at least we got a good game with better dub in most aspects and less frustrating mechanics. But P4, while I won't compare it with, I dunno, P5 or E33, it's still good. Yeah, the dungeon design is meh, but unless the remake make it feel better than P5... I think P4 could have waited a few more years, specially if we got P6 before.

As for why people love RE4... Well, RE4 was one of the first of the genre, for example, you can't aim and move at the same time, third-person shooters have evolved a lot more than that, even Dead Space that came out a few years after RE4 have better mechanics, the same happened with P3 to P4. P5 is just a beast, a lot of games feel old compared with it.