They likely do use mapbox for rendering maps, as their SDK is really customizable, is designed to work with the OSM data format, and you don't need to pay mapbox to use it (at least for older versions). But mapbox is not necessarily a good solution for all of the routing requirements Lyft has. For example, at SFO ride hailing drivers are required to wait in a special parking lot outside of the airport, and then dispatching for rides is done based on which driver has been waiting in that lot the longest. You could probably make this work with mapbox, but it isn't necessarily a matter of just plugging it in and calling it done.