Personally, I do think not having split screen in Forza is a pretty lame tbh. I very frequently played some rounds of Forza with a buddy coming over to my place, or vice versa, and I would imagine that it's probably one of the games in general where split screen would see that kind of use. Like, are there a lot of people who are gonna split screen a whole 100 hour game like Baldur's Gate 3? No. Are there at least a decent amount of people who would wanna be able to sit down with a buddy, or family member, and play a match of Forza, or a couple hours of Halo campaign or something? Absolutely.
I understand it's not a feature that's gonna be a big priority for most devs moving forward, but it's really a shame to see it go in so many franchises where it makes so much sense.