I remember watching a Vuelta three or four years ago that they did have police everywhere the fans were. They were pretty aggressive keeping the fans at bay. I even watched an official on a motorcycle just a ahead of the riders coming up a steep turn stiff arm a fan and send him into the ditch.
Maybe they were too aggressive then and caught some flak for it. I haven't seen as much of that going on. Don't even see as many Spanish Police on the Vuelta's routes since that race. Maybe 2017 or 2018?