Restaurant driver is not a highly paid or long term job, so I wouldn't expect the incidence of this is actually any lower amongst restaurant employed delivery drivers.

Like you say, it is a job, though, and not gig work. I don't know what it's like now or everywhere but I did delivery work in the pre-app era. I got an hourly wage, cash tips and one staff meal per shift. That's what often happens when you get employed by humans who have to look you in the face. They treat you like a human.

It would never have occurred to me to take bites out of customers food but if you see just how little these app drivers earn and consider how little loyalty they feel to any one restaurant or platform, it's kind of understandable.