I think on a similar question here on HN the most common answer was that it's a good gimmick to get people use Gmaps / Apple Maps. But with the recent news around Facebook acquiring mapillary I think it's hard to believe that it's just a gimmick.

Is Google/Facebook Etc. using street level imagery for something else? Training AI? Building 3D maps with ML? Making photos of roads in the entire world seems pretty expensive just to get more users for your app.