User blog comment:Cpt. Riley/Infinity Ward Co-Developing MW3 w/ Sledgehammer/@comment-174.45.238.91-20110124132426/@comment-1786471-20110124190600

I don't think they could trust the community to find all the bugs and the exploits of MP. I think they would have played the beta because they wanted to play the game, not to help the development of it.