This antagonism is not just jealousy. A lot of the same software engineers who revile Microsoft have warm feelings about IBM that go way back to the days when Big Blue was easily as dominant as Microsoft is now. Distributing the operating code won't help that problem. Simple as that. There's no boss there to make them do it, they do it because they love it and believe in the project they're working on.
Nobody believes in Windows.
It is a horribly hacked together system that is far inferior to our baby, Linux. Perhaps you'd get a few people chipping in some Windows source, but the development energy would still be spent on Linux, making it more powerful, easier to use, etc. It is simply a superior OS and I don't think anyone in the community would shed a tear to see Windows go the way of the Dodo. Jason Filby wrote to tell me about ReactOS, a similar project. But it's always fun to speculate.