These people are not protestors. There were rioters who would mix in with the protestors and then start violence. Protestors don't show up dressed in all black with a helmet and baseball bat.

They have also been allowed to throw bricks, molotovs, bats etc on law enforcement and people. They are destroying the peaceful protests to turn them into violence. Local law enforcement hasn't been doing anything to stop it because the mayors have been useless. That's where the feds intervene - especially because most of these people who are getting arrested are crossing state lines and therefore federal.