For Schermionie's 5, 10, 20, 50, 70, 100 Fandoms Challenge.
Blake doesn't expel Andie because he thinks she's obnoxious. It's not because he finds her dancing atrocious. And it's not because he doesn't think she was ever good enough for the school to begin with. Of course, it's true that she is a bit obnoxious. And he does find her dancing atrocious. And she never was good enough for the school. But that's still not why he expelled her.
He expels her because, contrary to popular belief, he loves Chase. Chase is his baby brother and when he walks into school with a black eye and wincing at every step, Blake wants to punch something.
When he asks Chase about it, he shrugs him off.
He keeps an eye out, though. Someone's got to know what happened.
Then he sees Chase talking to Andie West and it all makes sense. Andie, who hangs out on the streets. Andie, who learnt everything she knows on the street. Andie, whose friends are from the streets. Andie, whose enemies are from the streets.
Some people might say he jumped to conclusions, but it makes sense to Blake. Chase is involved with Andie West and he got jumped for it.
When Andie takes it upon herself to take the fall for the destruction of the studio, Blake seizes his opportunity. It's easy to justify to the board and anyone else who might care to ask; her involvement with crews endangers the school.
But that's not what he's thinking when he says, "You're expelled."
He's thinking that this is the easiest way to get some distance between Chase and Andie. That maybe the distance will split them apart for good. That Chase will be safe.
Really, he's not selfish. He doesn't expel Andie because he wants to. He does it for Chase, his baby brother.