From my experience if there is one thing arrogant musicians hate it's when someone is much better than them, more specifically, connects to the crowd much better than them. They have a music degree and play a lifeless, but perfect, classical piece and the crowd ignores them, then a guy comes out playing something joyful with three chords on a shitty guitar and the crowd goes wild. They hate it.

Since the Godawful screeching they subject people to five times a day is as close as they get to music, destroying the instruments of real musicians makes perfect sense.