Yeah, but protestors are frequently arrested and charged with completely made up charges. It is just a tactic how to discouraged protests. The cops doing arrests know about it, prosecutors know about it, defense layers knows about it and protesters know about it.
It has nothing to do with deterring crimes or crime rates, it is just politics.
The DA's resources are limited (unless all the Republican critics want to pay more taxes!). Arrest is enough of a deterrent for minor crimes.