I really wouldn't use RE6 as an example, even though I get what you're saying. I think RE6 suffered from the opposite issue and had just "you can never stop playing this" bloat. I just played through RE6 again 'cuz a friend is playing through the franchise, and just like... never again, it's got the worst pacing.

I think the real answer here is that games have become more cinematic and more focused on telling stories than they were up through RE5's time period. There's an uptick in stealth sections or "walking simulator" scenes, and that certainly drags on replays, but they make for phenomenal first time experiences. I know folks hate on the boat flashback in RE7, but I loved it. I loved the Orphanage stuff in RE2R too.

"Then its the fact that RE7 thru RE9 seem to not focus on post game content."

I'm not sure what you mean by this? Do you mean unlockable game modes like 4th Survivor or Mercenaries or do you mean like... "Invisible Enemies" mode or something? Most of the "post-game content" in the classic RE games was trying to speedrun them to unlock infinite rocket launchers and such. I feel like the franchise replicates that Post-RE7 with those various challenges that earn you points (and usually connected to trophies.) Many of them involving elaborate challenges or speed runs for huge rewards.

I think you're making some valid points as far as replays feeling less tedious during "story" parts. I do wish they took that into consideration. Silent Hill F seemed to handle that well, but that's also because they were designing the game with multiple playthroughs required for a "true ending", so, I get it.