One issue is that the scattershot visa applications from body shops crowd out applications from employers who want one specific, highly skilled person.
If skilled foreigners accept lower wages because the right to come to the US is worth something to them, then the price of the visa would settle at around the difference in wages. So overseas workers wouldn't undercut US residents. And the perceived monetary value of living in the US would accrue to the government, not to body shops.
This article seems to suggest that there's lots of small players competing over marginally profitable locations. There's also a negative externality which can lead to these people destroying their whole business: as people compete over machines that don't make much, they cut costs by not refilling as often and not maintaining the machines.
This means that the general level of trust in these machines goes down. After you lose your dollar a couple of times you stop using them. Aside from trusting official Coke or Pepsi machines, there's no brand loyalty (to the operator - a random name on a small sticker on the machine). So if your machines are well-stocked and in good working order, you won't do any better than anyone else. And after a while there are broken vending machines everywhere, which everyone ignores.
If this business is so lucrative, why isn't organized crime involved? It seems like a field where they have a number of comparative advantages:
1. Good at negotiating with local businesses.
2. Good at motivating low-paid employees to handle large cash sums without pilfering.
3. They love cash businesses.
4. More tax efficient than people doing 'side hustles'.
5. Good at managing kick-backs to eg. motel staff.
My guess is that the most 'gold mine' locations are already controlled by entrenched players who defend them using a variety of legal and illegal methods - vandalism of competitors' machines, high rents, kickbacks, threats to landlords.
Then all the marginally profitable locations are competed over by amateurs who routinely lose money and get disillusioned.
I think these businesses are impossible to scale because of the trust issue. You can pay someone a decent wage to empty the machines but you lose all your profits. Or you pay them rock bottom to drive around with thousands of your dollars in cash and merchandise. Then they rip you off in various plausibly deniable ways.
Everything seems to suggest that this has already happened. The reason this works as a 'side hustle' is because it's only lucrative if you ascribe a very low value to your time (and your car mileage, and the stress of doing admin for your 'business').
The fact the big players don't bother, the number of 'entrepreneurs' doing this in their spare time, the fact that they repair, move and restock the machines themselves, the calculations which ignore the presumably high risk of vandalism or theft, the presence of a landlord who can charge you as much as they like. And finally, the existence of 'mentors' who will charge you to be taught how to replicate their business.