The major companies that have tried to go faster than Waymo have been destroyed by safety incidents (Uber, Cruise). Waymo's caution may be well-warrented.
Because they're careful? Especially after the recent Cruise debacle - SF is relatively friendly to their efforts, and once they can point to a few years of problem-free operation in SF, other cities might allow them in, but trying to expand the service too early could prove a very costly mistake if a major issue is found and they get thrown out again...
Ignoring the safety path, this other issue just scale. Manufacturing the cars would be a big problem. Getting a ton of them on the road is another. I wonder if all those sensors that the car uses could ramp up to a national level in a year.
I've been in the Waymo beta for a couple months now. At peak times, it's more expensive and slower than an Uber simply because there aren't enough cars on the road.
I doubt that fees are quite covering expenses yet. I expect they'll roll out quite a bit quicker once expansion decreases their losses rather than increasing it.