Earlier quoted context omitted.
They work (most of the time) in Phoenix and SF because they've mapped every single inch of the cities by now and there are no adverse conditions. It's not scalable.
Why is that not scalable? Mapping out two large cities for an experimental project in a few years seems scalable, expand to new cities over time with additional resources.
Or perhaps my threshhold for “scalable” takes different parameters and weigh these inputs differentfly from you.