This way, everyone could benefit from the experimentation and likely some of their ideas would get rolled into the root project once they have proven themselves.
Forks are not particularly fun from the user's standpoint.
We've had a few forks of our projects over the years...most often, there's just one initial commit with a few minor changes and some big words about how cool it'll be when the community can steer the ship...and, then nothing, forever. The thing about forking a big project is that it takes a lot of time and effort to make it better, or even significantly different, from the project you're forking. "Do not fork lightly" is good advice, but mostly because it's gonna be a waste of time in most cases.