Why do graduate students spew a bunch of crap out during cl?

I feel like the students in my cles only speak outloud to hear themselves talk and almost nothing they have to say is intelligent or even relevant to the subject at hand. Speaking in cl is no problem, but irrelevant commentary is rampant! But nobody calls them out! Why do grad students do this? And if you are one of those students who talk just to talk, why do you do it? If they are as smart as they think they are, why can't they just save the bull for their papers and censor themselves a bit?