You can contribute to the project by using an app like NeoStumbler (GitHub) or Tower Collector (GitHub) to submit location reports. NeoStumbler does Wi-Fi, Bluetooth and GSM, while Tower Collector can only do GSM cell towers. Both are FOSS and available on F-Droid.
It is hard to have both; but not impossible. You can still be privacy friendly without sacrificing necessary functionality.
It will require that the "provider" of such a dataset constantly scrub, sanitize and remove data that would cause privacy hazards as quickly as reasonably possible however. That in and of itself is a technical challenge; though not impossible.
beaconDB doesn't log location requests, and it anonymizes location submissions, making it much more privacy-friendly than Google's or Apple's location services
So, you are willing to give your location to Google anytime any app asks for the location permission?
A lot of people is not. And there's been efforts over time to get privacy-friendly location services. So there's clearly demand for this, even if it's still niche due to lack of knowledge.
Ideally there's not a whole lot of data that needs to be kept.
Legitimately all that needs to be stored is a few things:
Location (GPS)
SSIDs (Wifi APs only)
Cell ID & MCC/MNC (Cell Towers only)
and things they MUST NOT STORE OR SHARE like:
IPs of contributors for longer than a few days
un-hashed BSSIDs (Wifi/BT)
MAC addresses (Wifi/BT)
IMEI/IMSIs (or other cellular identifiers derived from them)
APs that don't exist in a fixed location (Think mobile hotspot SSIDs) for longer than a fixed amount of time.
BT devices
Non-unique SSIDs or IDs that may indicate no user config took place and manufacturer did not differentiate device ID. (Things like "SETUP" with no unique number (SSIDs like"SETUP-be3fd34d" would be valid) or "[ISP]@HOME" or "[ISP]Wifi" which provide no meaningful discriminators)