Saving a fistful of cash is not worth you possibly losing your life.
I can see your point, but as far as the clerk in the video is concerned, his life was in jeopardy the moment the robber's gun came out. The guy can be so hopped up on drugs he's liable to shoot the clerk if he thinks he's moving too slowly.
In this setting, the bad guy may decide to start shooting everybody in the place, so other customers also have a stake in the results.