They haven't u-turned, they have delayed implementation.

This is a prime example of enshittification. What do Unity's users benefit from in exchange for this new charge? Nothing - all this does is increase Unity's income.

The reason they need to change their income makes sense - their primary income comes from helping mobile game makers push ads and that is both volatile and threatened by privacy pushes by Apple on particular.

The commercial motivation makes sense, and yet another example of how it leads to enshittification of a service or product.