They do it because they CAN. Why do you think they enrolled in the police in the first place? I would be ashamed to be one of those cops, or related to them. The violent reactions in those cops are so regular, so unprovoked and so asymmetrical that they cannot be "by chance" those guys really enjoy pepper spray people in the face. They probably can't wait to have a protest so they can finally dress up like the fascist thugs they are and do whatever they like.
I'm really surprised this is starting now. I thought that they would just wait out the protesters until winter in the hopes that they would leave. I mean I live in NY and have gone to NYC and the people there freak out and go buy a full NorthFace snow suit when it's 30 and a half a foot drops.