The level of policing was (in part) due to "intel" about likely animal rights protesters. Also, it surprises me how heavily the lads and lasses attending this sort of event booze, resulting in the peacocks 'avin' a barney.
These zealots are playing everyone for mugs. They glue themselves to things and know the police will remove them and enjoy the publicity. So why not leave them there, because they put themselves in danger and if they get hurt they would not do it again.