It's mainly an alumni thing. If you're smart when you go to CalArts, you'll make friends with all of the teachers, and all of the other students in your class. Then when one of those friends manages to score a job in the industry, they'll hire you instead of some rando from another school because you were their friend. This has been going on for a long time, which is why a vast majority of influential people in the industry are from CalArts.
Granted not ALL of the important people are from CalArts, Rebecca Sugar and Ian Jones for example, but the whole thing has still left a bad taste in the minds of other creators who weren't rich enough to attend the school.