I think you can only rollover if you close the 401k. Otherwise, nobody would pay the ridiculous 401k fees, or would just keep very little balance.
Believe it or not, we just switched from Mass Mutual to the much hated John Hancock. While John Hancock does suck, Mass Mutual was actually much worse. There were high cash balances in every investment option AND fees of over 1% on most of them, BEFORE the 401k "admin" fee (the hundreds of thousands they take every year for having put up a website).