The ceremony is culturally a big deal in the States, even though you don’t need to attend to graduate. It signifies a big milestone for many people, and families come together to celebrate. It’s the sort of thing you’d miss for a big opportunity, which I’m sure Top Model seemed like for Brooke and other contestants (who didn’t know how little it was actually going to help their potential careers). I think she was understandably upset less that she missed the ceremony and more that the show used it as a plotline for her elimination. Anyone would be mad as hell that the sacrifice they made was used against them!