Are you sure you're not talking about gig workers as well? For instance, uber says[1] that they need a valid drivers license and conducts background checks (which apparent check for previous driving infractions as well as criminal history).
And as a response to your perceived "gotcha", no, they do not need to be illegal. Even a refugee with a medical degree in their home can arrive here and can fall through the cracks in our system just because they aren't able to master a second language fast enough. Not every immigrant is illegal, no matter the pearl clutching.
I'm referring to people whom are given the same legal benefits of being able to work besides me when they haven't gone through the proper channels of legalities nor sought to do so. I remember my parents immigrating to the US and not have to cross a river at night with just the clothes on their back or pay off a "coyote" to do so.
For example, GigWalk.
You'll notice this pattern lots of places. Look around in employment ads for construction gigs in lots of cities and they'll be looking for 'contract' teams which we all know likely means some illegals who setup a genuine LLC or get a TIN or whatever; there's no requirement to verify legal employment when paying out a contract AFAIK.