What one needs to remember is that your college audition is not just the few minute you’re in the room singing and doing your monologue. It starts when you arrive on campus (or the hotel for unifieds) and ends when you leave. Programs are watching you to see how you interact with the people checking you in, the other auditionees, how nice you are to the accompanist, and so on. Most programs have current students around hosting, and they are providing input to the faculty on how well they see individuals fitting into the program.
So if you don’t have a long conversation in the room, part of it is the limited time to do so when you have so many kids to hear. But part of it might be they already know you won’t be a good fit for their program based on the interactions you’ve had the entire day, or that they see you as a good fit.