That's true, but there might just be people who wan to play the "best looking" version of Call of Duty, or Madden, or Assassins Creed, or whatever their game is, and that might be enough for those folks. Like you say, Ubisoft doesn't really care if you buy the Series X or 1S version of Assassins Creed. They're not trying to sell new consoles for anyone, but at the end of the day, I think there will be people who buy a new XBOX this fall just to play the prettier versions of those games. Like, if all you play is Call of Duty, I'm not sure Microsoft's (or Sony's) 1st party line up is going to factor into your buying decision one way or the other. On the other hand, if you just wanted to play Halo, then I don't understand why you would buy a Series X in 2020.
I also don't think that most of the game buying public really sits around an analyzes this stuff the way we do.