A number of startups did this in 2017-2020 (Scape, Mapillary, Niantic, google, apple and a a few others who's names I've forgotten)

With consumer cameras and GPS you can make pretty good maps, vaguely automatically. Keeping them up to date was mostly down to making sure that you had enough overlap in the data at different times.

The big thing for that generation of companies was AR, and making AR games accurate. This also had a feedback loop of people uploading photos/points to update the map.

With this system, I'm not sure what the point is. I don't get free maps, and frankly they are commodity now anyway.

Personally if I was going to do this again (I'm not going to because meta/google would crush me in an instant, also there isn't a market for the end product) I would pay delivery companies and security people for the data, or operate a CCTV "inteliigence" platform and generate the map as a side effect.

If you want to make your own maps, its acutally not that hard: https://github.com/cvg/Hierarchical-Localization is the more advance and less user friendly version of colmap: https://github.com/colmap/colmap