Here is a mildly informed reason why applications dropped:
https://www.sanluisobispo.com/news/local/education/article222264700.html
Basically it says that Cal Poly was less active in seeking student growth, since it wants to reduce enrollment which I am guessing translates in fewer promotional activities to generate applications.
Painting an entire student body with a smelly brush based on the reprehensible actions of a few dumb headed individuals feels like a bit of a stretch to me.