Theo didn't give a fuck what his roommates thought about it, and the social balance of the Slytherins was too disrupted for any of them to say something about it to him. Draco was clearly out of favor after he'd fucked up the year before. Crabbe and Goyle, ever the followers, needed someone new to report to, but they didn't trust Theo enough to listen to him and so they remained helplessly adrift.