I am not sure what you are trying to prove with this comment? If someone did some cheating they should be suspended as well and be punished. But some comment with no basis in fact and different from what the Astros were doing isn't much of an argument. I am not sure why you are using it.
It hasn't been confirmed that Davis put on 25 lbs of muscle, correct? Davis looks more ripped for sure, but he's almost 34 years old and putting on that much muscle (naturally) in one offseason seems like a bit of a stretch.
Strictly an economic/efficiency ploy. Won't have to staff those areas during games, or clean up after the game. Also forces fans to sit in higher concentrations in the open sections which could look better on camera -- if you care about vanity.
Any trainer? I don't see any of the trainers at the gyms I have gone to looking like Davis. If it were so easy than the trainers would all be jacked up. Most of them have less muscle than me. Let's us not make stuff up and act like it is easy. I know people that are gym rats and don't build any additional muscle size.