Because Michael Bay is an arrogant ass. This is common knowledge.
The reason he gets jobs is because he can bring films in under budget (ironic) and on time AND they make money at the box office... Even if not in the U.S., but overseas like with 2004's "The Island" which tanked here, but blew up in Europe and Asia.
What people don't like about Michael Bay is what I said above: He is a pompus jerk who thinks he is God's gift to film making when he is not. Also, his attitude toward movie going audiences is they ARE dumb and are nothing but "horny teenagers" (quote from an actual interview) -- Even if the audience for his films fit this label, he doesn't have to be so condescending... Which is where the label of him being an arrogant and pompous jerk come from.
Also, his style is terrible. He uses a lot of cheap parlor tricks to make up for the lack of his actual directing skills which is also why people cap on his films so much because again, it is true.