I saw Lucas say on Facebook that Natty Boh probably wasn't willing to pay the standard fee for getting their beer in the park.
But sure, the concessions aren't good overall. I don't think the beer aspect is really a problem though, and you can bring in food, which is nice. Plus, a big positive of Camden Yards is it's downtown, so pregame eating options are plentiful.
A lot of people don't give a damn about pregame eating, especially when they have families.
It's part of the whole experience.
I don't agree with the reasoning myself, for many of the reasons you stated. That being said, there are a lot reasons someone would turn down going to the game and if shit concessions were one of them, so be it.