And since the state of the open source map rendering art is consisting almost exclusively of pre-licence-change forks of mapbox code these days, they kind of still are.

I wonder if Strava's recent acquisition of fatmap.com eventually boils down to them cutting ties with mapbox via acqui-hiring some mb-libre excellence. I could imagine Strava, due to the extreme map-centric nature of their product, bleeding quite considerable money to mapbox.