They started with a great idea. Let's give the users tools to create their own content. That was, depending on how you look at it, 15 years ago, 10 years ago, or 6. Since then they've been slicing the idea up into smaller bits, occupying ever-smaller niches, creating derivatives, mashing all that up, and creating more derivatives.
It's gotten terribly stale. The people are still brilliant, some of them, and there's tons of money available, more than ever, but they need some new ideas. This, unfortunately, is not something they know how to do.