Don’t think it has to do with class. Surgeons and dentists still need to show up to work. Even in tech, the higher up you are, the more likely you will want to be in the office.
Yes, the doctor making $350k/yr can arrange his life in such a way to be more flexible in the face of diversity, but he's just as likely to have $150k worth of school debt and a house/car/etc. he couldn't afford if he had to switch careers. At $7.50/hr, you can probably walk down the street and find a better paying job.
Edit in reply due to depth restrictions: I'm not suggesting this is about ease of switching careers. I'm suggesting that you will be forced to switch careers if you don't show up to work, and it's probably easier to switch between jobs with no prerequisites than careers with 8 years of intensive prerequisites and $150k in university.