> and for niantic to achieve good photogrammetry with their random collection of photos taken from different angles, on different days, etc they would need some kind of ground truth to train on, which is implausible.

I'd say... the versatility of photos provides the "ground truth" on its own when combined to one single dataset. Say you want to program a guided drone shooting through urban areas, you want it to work under all sorts of conditions - day, night, rain, snow, the sun visible from all possible angles and throwing shadows.

A dataset that you can get from something like Street View? You can at best generate that once a year at enormous expense. Still valuable because a Street View car likely has a multitude of highest-quality GNSS receivers and possibly RTK navigation aids, but to make the dataset usable for 24/7/365 navigation you absolutely need a huge, huge amount of backfill.