This really sucks. MVP was actually one of the most over guys in WWE, and as much as i'd love to say "it was a matter of time before he was pushed to the main event", realistically that probably wouldn't have happened either seeing as WWE neglected to push him when there were so many opportunities (ie, drafted to Raw and could've easily fueded with Orton).
He was likely not pushed because of his age (he's in his early 40's isn't he? Not exactly a future investment), or because, like someone said, they couldn't figure out how to market him, especially as a face.
At least he asked for his release rather than being fired. It was his choice. Knowing that brightens the situation a little.