The crowdsourcing part is what I meant. And you probably underestimate infrastructure as well.

This also isn’t something you can just let a few volunteers do once and forget about it. It needs to be something that people run often on their phones. Wi-Fi access points change, cell towers sometimes change. You need to keep this data up-to-date. With Google’s or Apple’s location service, when a person buys a new router, it’s probably added to the database within hours or days at worst.