Disney keeps going back and forth when it comes to video games.
One day they are closing their development studios. The other they remind themselves they own a big pile of properties and games, and start making plans to re-release them, or license them to other publishers.
Fortunately, I own almost all their games on Steam, especially the Tron games, since I like the franchise (and love the original film

).
Probably a licensing issue. Maybe some of the tech? The soundtrack?
Either way, it's a strange choice.
Hopefully, everyone who wanted it go it before it was taken down.