The Wine project apparently decided they wanted to keep alive an old version of a piece of software Microsoft has no interest in and Microsoft gave them the official repo instead of throwing it out.

Mostly interesting in that it is a token of goodwill from Microsoft to Wine something which is in line with the current Microsoft view of the OS market but would have been very surprising not that long ago.

It's not like Microsoft can force Wine to take the codebase. In order for this to be donated, the Wine project needed to accept it.

Pretty much, by the look of it. But we still don’t know everything or what exactly the Wine project has on its metaphorical mind.