It could be the case that certain games skip Xbox altogether because of the Series S. That's a gamble Xbox made when they made it a rule that every game must work on both Series S and X.thats cool and all but in the long run as games get bigger developers wont pay enough attention on series s versions theyll likely treat is as how they treated nintendo wii ports during ps360 gen, especially ue5 type of games
Another thing is that Series S has far outsold the Series X (we can speculate as to why) so even if developers made a game, put all their attention on the Series X and just released a shoddy Series S version with a bunch of issues... you'd have the majority of the fanbase with a sub par experience.. and that would generate negative press.
Some studios just might not bother. Fortunately for Xbox fans though, Larian is bothering.. but it will just take more time.