Hmm, those are the specific apps using Google Maps API. That's like saying why does HackerNews use jQuery, I want it to use lodash. (I don't know if they do, just an example).
Don't they just call the default maps sdk, whatever implementation it is? Because if I firewall google play services and some other google stuff, but not the app that uses it, then everything will work but the map isn't displayed. It's google play services that does the map loading, not the app, it seems.