The security in the video is very passive about resolving an obvious vandalism in front of them, why don't they like... Check bags at the door for Cans of Soup

The security in the video is very passive about resolving an obvious vandalism in front of them, why don't they like... Check bags at the door for Cans of Soup? Try getting between the painting and the glue people? Try saying "Stop" with authority? What are these security people going to do when somebody walks up to the wall and just takes the painting with them?