I really think this is a result of all the infighting that's been going on in the community over the last couple of years. I think a lot of people have either gotten tired of being harassed by other groups that they don't get along with or didn't agree with the rules laid out elsewhere, and have responded by shutting the doors and only allowing the people they want to have access to their sites/creations (if not just bailing out of Mugen altogether). We've seen this community go from a small number of large, active boards to a large number of smaller, mostly private boards (sure, the big boards are still there, but this scene is nothing like it was 3-4 years ago). A lot of people out there seem to either be paranoid over someone steal/leaking what they are working on, or are hiding from people they don't see eye-to-eye with.
I personally hope this trend doesn't last much longer, since it doesn't bode well for the future. The community can't grow if large portions of it aren't accessible to the outside world - a lot of potential newcomers will just get frustrated and walk away....
Veterans Day