The short answer? They're not proper survival horror games.
The long answer...well, I suppose I'd better elaborate. The problem with Resident Evil, and the AAA game industry as a whole, is that they arbitrarily decided that the survival horror genre was dead a generation ago and haven't given us a proper one since. We've instead had gun-toting, fast-paced survival action games. Whilst that isn't a bad thing persay - because survival action can be good too - it isn't what Resi is known for and, frankly, not what it does best. Others have picked up the torch and given us survival horror titles, sure, but Resident Evil has most definitely departed from that genre entirely.
There is huge, HUGE difference between Survival Horror and Survival Action. There isn't a lot of suspense to be found in a game where you just go around blasting the living crap out of everything that moves. Jump scares are an element of survival horror, but alone they do not make a game as survival horror game. From Resident Evil 4 onwards, the games have lacked that element of horror; it's all been about the action. You're not afraid to open doors because of what might or might not be lurking behind them, or jumping at shadows. You don't have to worry about conserving every shot, about whether you'll need it for the next enemy, because there will be more ammo just around the corner. The best you can hope for is that you might get surprised by a quiet enemy somewhere down the line. I think the only time I was genuinely terrified in Resident Evil 4 was when I was running away from the invisible Alien/Predator thing, and that was because it was invisible.
It's basically just like a zombie expansion map pack for Call of Duty. Again, that's not a bad thing. But it isn't Resident Evil. It's not survival horror. It's survival action, and the feelings those games invoke are completely different. I think the main objection is that it's just not scary any more, and it isn't because people have gotten used to it or can predict it, either. Part of what makes survival horror scary is that you can predict it to a certain degree after all, but you know that just because you can doesn't mean you'll be able to survive it.
...plus, Resi 5 killed off Wesker. That was like Metal Gear Solid killing off Liquid Snake. For me personally, without a proper villain, the interest is gone.