It's not about being the best player though. It's about being the most valuable. Cabrera was more valuable to the Tigers in the sense that they would be on the playoff couch without him. Angles couldn't make the playoffs even with Trout having one of the best seasons ever.
It would be a no doubter had the Angels made the playoff though.
MVP is for the most valuable player in the league. Not the most valuable player who's team made the playoffs. Several winners before have won it without their team making the playoffs. It's for the most valuable player in the league.
Second, Trout's team won 89 games. Miggy's won 88. So .... who's team had the better record? Yea, must be nice to play in a crappy division with the Royals, Twins, and Indians. After Trout was called up, the angels posted a .584 winning percentage. Better than anyone in their division. Second in the AL.
Third, Cabrera's claim to the MVP rests solely on him winning the Triple Crown .. which is completely dependent on RBIs. Which is completely dependent on what the hitter's teammates do. Austin Jackson doesn't have a monster career year with the bat and Miguel Cabrera doesn't even sniff the Triple Crown. Oh, and if you gave Trout twice as many plate appearances with runners on base (like Miggy had) and I'd like to see what kind of numbers Trout puts up.
Fourth, Cabrera's defense was actually costing his team games. Do you know why Cabrera's WAR is the same as last year, despite putting up better hitting numbers this year? Because Cabrera's defense was awful. He wasn't a very good at first. He was amongst the worst at third. Meanwhile, Trout is one of the best defenders in center field.
As I said, Trout had one of the greatest seasons in the history of baseball. And he did it in 138 games.