To be fair, I remember back in 2005'ish Microsoft reaching out to open source developer communities to help provide support for open source projects running on Windows. That was when I first remember thinking that it was interesting hearing from them at the time. I think it's not so much waiting until Ballmer was gone, but rather, it just took a while for everyone to take note of the changes. And, of course, that changing a big company like Microsoft would take some time.