However, all your "friends" are on it. Nobody wants to go back through that process on an upstart network. Nobody has the energy or motivation.
There's plenty of room for new entrants that take slices of your friends and optimize that experience. For example, another network for just your family... offering a close, intimate experience, one you feel comfortable sharing all your baby pics on, etc. Another network for professional (sorry, LinkedIn already there). Another for your classmates. All sitting under the facebook umbrella that has your entire social graph.
But one thing that's clear about facebook is they are not at all focused on improving the user experience any longer. They are not unveiling new features that improve user experience. They are fully engaged with improving the advertiser experience. Maximizing the value of the data they have on you. Maximizing ad revenue. These aren't bad things and are obviously necessary, but when a company seems 100% focused on the revenue rather than the user, I think that signals the start of a decline.