If they are making $500 a day, they only need this to work for a few months, then they have enough cash to keep them going for a few more to come up with another great idea.
I'm not sure it's sustainable, but it's certainly viable!
Or branch out... my experience with the French consulate was ... uncomfortable the first time, and I would have paid handsomely to not have to go back again for the same Visa.
I soon realized that the Consulate's job for many countries is to keep people out... only when I went to the UK consulate did I see an attempt at customer service.
In fact, any country without a US visa waiver [1] sounds like a decent target market, as all visits would require a trip to the Consulate.
I'm not sure it's sustainable, but it's certainly viable!