[Joe]

They let him off the hook because of his popularity and because he was MVP and they didn't want to go through the very public rescinding of a player's MVP award and the ensuing bad press. That would damage the game, and the league so desperately wants to put it behind and has for the most part.
Then he goes and starts thinking and speaking for himself when there are so many spokespeople available who could have put a much better spin on it.

**Addendum: I forgot the most important reason - they let him off the hook because the commissioner, Selig, just happens to own the Milwaukee Brewers.