Presumably Unity decided they had too many customers and needed to get rid of most of them. Not only is this an insane thing to charge developers for, there are all kinds of concerns like:...
One of the big winners of the Unity debacle is the free and open source Godot Engine, which has seen its funding soar to a much more impressive level as Unity basically gave them free advertising. Certainly helps that Godot ended up launching their new funding platform on the same day Unity announced their hated Runtime Fee...