No. 1 reason Mookie Betts could win MVP: Circumstance
Let's lay the whole case out. Acuña has been the better hitter on average. He's more explosive on the base paths and blessed with an arm cannon in right field. He is a walking highlight — the face of baseball's next generation. A lot of fans tune into Braves games just to watch Acuña work his magic.
Betts does, however, have a few things going for him.
First is the definition of the award. Everybody comes by their criteria differently, but it's the most valuable player award. Not the best player award, not the most entertaining player award. The most valuable player.
On top of the catch-all WAR metric, Betts has the benefit of outstripping Acuña in the field. Betts has toggled between right field and second base all season, flashing Gold Glove qualities. Acuña is generally weak in the field, with the exception of his throwing arm.
There is also the matter of team quality. The Braves (103-56) and the Dodgers (98-61) are only five games apart in the standings, but Acuña happens to play for the most talented team in baseball. The Braves had eight All-Stars this season, including the entire infield. The Dodgers are no slouches by comparison, and Freddie Freeman even outpaced Betts in the MVP race for half a season, but the Dodgers aren't as top-to-bottom dominant. Betts has less "help" in a sense. One could argue that Los Angeles would feel his absence more than the Braves would feel Acuña's absence.
It is hard to mount such an argument objectively, but voters generally let personal biases run wild. If voters believe Betts is more valuable to the Dodgers than Acuña is to the Braves, he could steal a chunk of votes.