Tesla itself uses HD maps for things like intersections, traffic lights and so on. It's just not at the level of detail others use it for.
They’re also offering a commercial service. Which means figuring out operations, customer service, emergency protocols, working with local administration and so on. They’ve said a larger goal in Phoenix is to figure out how to perform and scale operations. The local regulations there are much more favorable. Until recently, Phoenix was one of the only (probably only) places where you could operate a robotaxi program and charge for it. California just recently approved it, so SF is where they’ll likely go next as they are already setting up everything there.
Ultimately, mapping is the not the constraint for them to go to new places. It’s the operations and regulations that they need to figure out every time.
Well, that’s Waymo (in Phoenix) which has put out anything approaching autonomy, not Tesla. Tesla requires a driver.