The Cubs were a heavy favorite last year that ended up winning it all, but that's pretty rare in baseball. When the Giants won it in 2014, they were a Wild Card. The Royals made it in 2014 as a Wild Card, and nobody saw them going back in 2015. The Mets made it in 2015 after not even making the playoffs in 2014, or for quite a few years.
The team with the best record very rarely wins it all in baseball.