A sizeable chunk of .NET development happens in the corporate/enterprise world. That sort of environment isn't interested in collaboration, open source, etc.--they're interested in the guaranteed support the MS stack provides, and the idiot-proof web basics provided by ASP/webforms/MVC. If shit hits the fan in the .NET stack for a big enough corporate project, someone in the office can phone/email MS and get support…
Oh, please...
Over the years, I've personally fixed bugs. And sent in fixes. (Stop complaining -- I promise to send tests too, next time!)
If I run into one that I am unable to grok in a reasonable time, there are always job boards and money.
Bugs -- not to be confused with full sized features -- are generally not that big a problem in even non-popular open source. You don't have to decompile the damn code!!
And you can get bugs fixed without waiting for a new release, next year... maybe.