Generally, they are there to, perhaps, provide a deterrent, and as witnesses to any crimes that take place. They’re not there to intervene.
A - they get paid squat. These security companies are not hiring ex cops, or even bar-bouncers, as their security. Often, they are unskilled people who lack skills to get other employment.
B - they have nearly no training in dealing with a physical altercation
If they try and intervene, they are more than likely to just get their asses beat.
This exactly. Not sure what's so hard to understand about this. And you know what? Even if the guy was supposed to physically intervene, no one should put their own physical safety at risk for corporate profits.