The award is not for the best player, or the best player by advanced statistics. It's the Most Valuable Player. Value is a subjective term, and the voters, in their wisdom, decided that Cabrera deserved the award over Trout. Some people, i'm sure voted that way because of the Tigers making the postseason. Some voted for Trout because of his WAR, BAPIP or better defense or whatever.
There is no right or wrong to this argument. The voters voted on a subjective award and it went to Cabrera. You are allowed to disagree with the selection, but you aren't right and the voters aren't wrong. It's a vote.