Wouldn't be that certain... there is a lot of stuff built on Unity. The most common theme I heard was that they're trying to capitalize off of Genshin Impact [1], but there's also a ton of other highly successful games like Among Us or Untitled Goose Game that won't/can't (easily) be ported to another engine.
In other words, they want to become the IBM of game engines. Rent seekers for sub-par service.
[1] https://www.sportskeeda.com/esports/will-genshin-impact-affe...
[2] https://www.create-learn.us/blog/top-games-made-with-unity/