> OpenStreetMap is not supposed to be directly used by commercial sites. Not if I understand their terms correctly [1] [2]. Maybe there's a distinction between the terms of the map data itself and the software published to interact with it? [1] https://www.openstreetmap.org/copyright [2] https://opendatacommons.org/licenses/odbl/summary/
IIRC that's for the openstreetmap.org site, which wasn't built to answer queries from hundreds of commercial apps (like Maps API is). You're supposed to copy and deploy the dataset on your own servers so you don't burn bandwidth of the OSM project.
And there's several other places that offer this as well. So the advantage of building on OSM data and APIs potentially is that you could switch providers without losing API compatibility or having the data available change out from under you.