I think Netflix doesn’t want to be on AppleTV because it messes up Netflix’s recommendation system.I thought the real reason Netflix is not joining the TV app is the fact that Apple gets to keep viewership data that way, which was something Netflix was heavily locked down on for a very long time (they only started giving out numbers a year ago afaik?).
I honestly don't even want Netflix to join the TV app anymore, I got used to having to use 2 apps now (TV app and then Netflix separately)... what really grinds my gears is the fact that they still didn't even acknowledge SharePlay functionality. I wonder if they one day add support for that... they're like the last big streaming service without a group watch feature? There's really no excuse to not implement SharePlay support because it's dirt cheap to do so, all the heavy lifting is done by Apple via FaceTime.
Netflix would still know what you’re watching because you would be on the Netflix app anyway. It’s just that Netflix won’t be able to recommend its own shows while you’re on the aTV app.