The way that I heard it was that the Cartmen owners leased out the carts to the drivers. The drivers were the ones who couldn't make a profit because of not getting paid. Cartmen got money, but then ended up not getting money when no one wanted to drive for them.
Also, I was under the understanding that the owners also received a grant for their business.
The reason that they didn't charge a fee or a fare was because they didn't want to be governed by the same rules as cabs. Otherwise, they could have gotten around not receiving any tips by charging a minimum fee for transport.
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