I can see the point that having to also port games to last gen will take away time that could have been spent optimizing for series s, but I also do wonder if that extra time gained will be negated by games becoming too complex to easily run on xsx or PS5 anyway. I can't be alone in thinking that these days of games regularly having almost native 4k won't last forever. Someone at some point is going to start pushing graphical fidelity at the cost of resolution/fps.
The point is that few people on Series S buy games to begin with. Meanwhile PS4 still sells loads of games. Given how expensive game development is, it's only logical to sell to a huge userbase rather than a small one. People who buy a Series S and gamepass don't buy many games outside of it. For now many games with an old gen port are mostly PS4 games which are ported to PS5/XS with extra bells and whistles like Resident Evil. Those games still look rather good, look at RE4 remake for example.
It's games like Hogwarts Legacy that will be the problem. Especially games similar in scope, but nowhere as profitable, since less profit also means less investment in the product. Subpar optimising for XSS can reduce investment costs.
Please excuse my (probally) poor grammar