Apple does Apple things and heavily restricts third-party developers.
Fleischer, having dealt with malarkey like this for close to a decade, realizes he doesn’t get paid enough for this shit.
He makes the repo closed source in 2017, but doesn’t mention this to anyone.
In 2019, after making a bunch of critical changes to the code, he quietly announces that the licensing terms of the project are now different.
At this stage in the proceedings, companies’ choices are to pay up or tell their users that they can’t use the hot new version of macOS.