Because there's only Mr Zuckerberg running the whole company?
He's been at it a while. If he gets beaten I don't think it will be to do with youth and inexperience. Remember Google failed with their first offering in this space (Wave), was it youth and inexperience then?
Wave wasn't really designed to be a social experience. During the keynote, they talked about what Email would be like if it were designed using today's technology, rather than evolving from snail mail. What they came up with was a lot of very impressive technology. They gave this technology to the developers in beta to see what they could do with it. While Wave was scrapped, bits and pieces of it live on everywhere from Docs and Calendar to Google +.
He's been at it a while. If he gets beaten I don't think it will be to do with youth and inexperience. Remember Google failed with their first offering in this space (Wave), was it youth and inexperience then?