Every teenager who has ever had a job at a convenient store/fast food/restaurant/hotel/etc knows this. Enough of the population simply likes it because it keeps prices low for them, and maybe some of them justify it themselves by having been already subjected to it.
Not to mention that calling a 19-year-old "manager" and maybe giving them a different color uniform shirt is a good way to get that 19-year-old more engaged in the job, that doesn't involve any extra expense on the employer's part.
