I think you are missing the point Taxi companies in Baltimore already have a regulation that they can't discriminate. They ignore it, there appear to be no enforcement consequences for doing so so why would they follow it?

Uber has no such regulation yet people who use it report having an easier time getting a cab in parts of town Taxi's discriminate against.

There are several things Uber does that make it less of a problem for them. Drivers feel safer since the interaction is pre-vetted through Uber. It's cashless so not much to rob. You know the person you are going to meet must have it together enough to have a functioning credit card, smartphone, and cell service.

Uber removes drivers that decline too many fares (good drivers accept like 90%). When a fare is offered to a driver they only have 12 seconds to accept it and they only show the driver a very zoomed in map of the location and the estimated drive time to the location. So even if one driver is discriminating the offer will be quickly routed to the next closest driver until one accepts it.