Why do you think this is fraud?

At least in SF, I'm pretty sure the standard deal is that the drivers pay for the cab regardless of what they get in fares. Cabs were a cash business for a hundred years, after all.

I think the deal with credit card machines in the cabs is that the cab companies see it as a revenue source. I know cab drivers grumble about the cost of using them. It makes sense to me that Stripe is cheaper for the cab drivers.