Larian has delayed the release of Baldur’s Gate 3, currently on pace to possibly be 2023’s Game of the Year, until they can figure out how to make split-screen work on Series S.
If they’d taken the Series S as the base line during development, they would have made life a lot easier for themselves.
The problem is that the baseline is actually the PS5. It outsells both versions of the Xbox by a factor of 2. So the Xbox Series S is an afterthought, and always will be.
It would be to Microsoft’s advantage to change that perspective, which would reinforce why they might maintain their hard line of feature equivalence. I agree though, it appears to be the status quo.