I haven't built any apps for contributing to beaconDB as of yet. The website links to NeoStumbler and TowerCollector, which are Android apps that can be used to collect this data.
It is rather surprising how many people have started contributing already. I believe that people want to support alternatives to big tech so they aren't completely reliant on these providers, and beaconDB is currently the only database not owned by big tech. Not 100% sure that answers your question :)
The developer might be open to add other services since MLS is being retired: https://github.com/zamojski/TowerCollector/issues/223
Doesn't hurt to contact them/make suggestions on this issue.