Sales and installs don't happen at the same time. If I buy a game once on Steam, I might install it on any number of unique devices. Per the Unity FAQ, every one of those installation events results in an additional bill for the game's developer.
In other words: This is absolutely a retroactive rug-pull on new installs of old sales.
Update: Because of the way they're rolling this out, the only way to avoid the retroactive license change is to immediately stop using Unity's development tools. If I were running a game studio, that's what I would do.
In other words: This is absolutely a retroactive rug-pull on new installs of old sales.
Update: Because of the way they're rolling this out, the only way to avoid the retroactive license change is to immediately stop using Unity's development tools. If I were running a game studio, that's what I would do.