for the same reason as when someone suggested Ron Paul buy the Daily Paul.
If he is actively involved it could become seen as "Ron Paul's" site, meaning people can dismiss the content as being biased by him. The way it is now it was created strictly grassroots and remains so. That's actually powerful, because there is no need to censor or spin anything. What you see is what you get.
He is starting RonPaulChannel.com so that will be plenty of Internet presence I think :)