Considering the expense, and especially time, involved in gathering street-level data, if I was Apple, I'd put every sensor I could think of on those cars and then let the data scientists figure out a use for it later.
Colossal bandwidth use for very high latency updates? Surely it’s better to get depth information from the device rather that from Apple’s self driving cars/StreetView clones, either with stereo, lidar, or AI estimates?
tl;dr they're using it to make better maps