How common is it for bartenders to get drunk at work?

Genuinely curious how common this is cause I’ve heard my bartender roommate say she and her coworkers are always pretty hammered by the end of their shifts. There’ve been some times where she even says she isn’t planning on getting drunk that night because she has something important in the morning but ends up stumbling home anyway. She says it’s pretty much the norm for her and her coworkers. Is this common and why is drinking on the job so hard to resist?