Because Wine often needs to run .Net applications and Mono is the easiest way for them to do that.

they were already maintaining a fork of Mono for quite some time. This seems to me like a ceremonial torch passing to make them the ‘official’ owner of the project.

while you might be right some things are more important. why is your comment not directed to people actively blocking these changes? why not just agree to them and move on with these “more important things”. the PR was submitted. the effort had been done already. blocking it is an statement on its own.