Unity is used by many mobile game studios in the developing world who don't follow Western accounting practices. It would have been hard or impossible to get proper Unreal-like revenue sharing out of them.
The correct move would have been to ignore them but instead Unity chose to shoot their other users and themselves in the foot.
Or, you know, they could have done the normal software thing of charging once for the tool.
But yeah, this would have still have meant that most of the developing world devs would not have paid...
I'm guessing here is that Unity counts on these devs being forced to go through a few game distributors that have monopolized it in the developed countries : iOS, Google Play, Steam... this is a bigger issue here !
The correct move would have been to ignore them but instead Unity chose to shoot their other users and themselves in the foot.