One big challenge there is that infrastructure is expensive; replacing it moreso. To use an analogy, it's a lot cheaper to replace trains in a rail fleet than

One big challenge there is that infrastructure is expensive; replacing it moreso. To use an analogy, it's a lot cheaper to replace trains in a rail fleet than to replace track (the per-unit cost might be lower, but the logistical cost of downing a track network to switch it out can be significant, especially in last-mile areas or bottlenecks). Horseless carriages drive on roads that were minimally modified from what the horses used (in some parts of Pittsburgh, for example, they never swapped out the Belgian block).