Originally Posted by RatherBeOnATrain

I suspect that these incidents happen because the TSOs are effected by some type of Bystander Effect (Wikipedia) and/or other social psychological phenomenon.

The combination of having (1) so many individual TSOs staffing each checkpoint and (2) having them spend the entire workday doing and seeing the same thing over and over and over and over and over and over outright guarantees that individual TSOs are not likely to take action when action actually needs to be taken.

In other words, if an individual TSO realizes that a particular passenger needs to be stopped, that particular TSO won't bother to do it because he/she will figure that another TSO (standing closer to the passenger) will do it.