Because it creates a bottleneck that limits game design. For me it's got nothing to do with console wars, I just want the games to be fully unleashed by not having to work on older hardware, in so many ways that surpass just having better lighting or shadows.
I want the big tentpoles to be next-gen exclusives, so they can push the envelope, but indie games or smaller experiences are fine as cross-gen. If your game doesn't have elements that simply would never work on older hardware, then by all means.
I agree with this.
You know, what strikes me as something not really spoken of here, is that I think for most people disappointed right now, it's not that we don't want or expect there to be ANY cross-gen titles. Some titles make sense to be cross-gen. Some titles are missed opportunities to be cross-gen as well even, like Gran Turismo 6 on PS3 in PS4 launch window, what an oopsie that was in retrospect.
But look at PS4 launch window games, Killzone Shadowfall, Knack, Infamous Second Son, and beyond, Sony 1st party was almost exclusively devoted to making PS4-built titles, with a few exceptions where it actually made sense. Third parties are OF COURSE going to go ham with cross-gen, which is what makes it all the more exciting to actually see next-gen titles not crippled by old baselines.
It also makes for some interesting switchovers when third party franchises jump to next gen. The difference between 7th gen baseline Assassin's Creed, COD, Watch Dogs, etc and titles built ground up for 8th were pretty robust, with some growing pains like with AC Unity lol. And who can forget the heroics of taking 8th gen games and cramming backports to weak hardware like with Titanfall 360 (based Bluepoint, holy hell) and Witcher 3 Switch. I know Switch is technically 8th gen, but let's be real and call it 7+/7.5. It's way down on ram, I/O, and GPU, but with better features and not limited by half a gig of system+vram.
Hell with Switch, that's why WiiU cross-gen ports are so well received starting with BOTW. If Switch was a set top console only with that power deficit, it would rightfully be laughed at, but people understand the inherent limitations of being a handheld, and are willing to accept the compromises. What would be pretty pathetic for a set top $299 even in 2013 is pretty impressive for a handheld under any reasonable metric.
Coming full circle, if ONLY Sackboy and a couple of other minor 1st party were cross-gen from launch onwards, there would still be at least a solid couple of years of cross-gen led by Ubi/etc. I think that's what everyone was expecting with PS5 and the previous messaging about building new potential with the SSD and cast increases in I/O, level design, CPU and AI, etc. You'd have the heaps of cross gen third party for the first couple of years, and then a handful of 9th gen exclusives.
But now? It seems like almost everything so far is cross-gen, other than Ratchet and maybe God of War. Demon's is obviously a PS3 title, and however impressive, is just a dressed up game with prettier graphics and faster loading. Not entirely a bad thing, but a PS4 version would have totally been doable, no question. Spiderman Miles and Horizon are now PS4 titles, PS5 will just be prettier, faster loading versions of the same title. And for how long afterwards? After this, it seems many expect that God of War is not even designed around PS5, whether or not they actually have a PS4 port planned. The backlash may get them to lean towards cancelling a PS4 port, which I actually feel would be sad and the wrong move IF they've designed it as a PS4 baseline game this entire time anyway.
We don't want PS5 exclusive games just to crap on 8th gen. That's not at all what this is about. It's just that 8th gen already had barely any more CPU power than 7th gen to begin with, and now it's kind of been since ~2005 that we've had game design limited by fairly low hardware/game AI and scope potential, just with ever increasing textures and resolution. 8C/16T 3.6+GHz Zen2 and 50-100X faster storage makes for a gargantuan increase in what could be done with that level of baseline, and having to wait even longer to see very much of that is suboptimal.
EVEN Ratchet, PS5 exclusive that it is, has to kind of make sense as a game that plays by old era Ratchet and Clank rules.