For example, while Mapbox use open source (OSM) tiles, other services - e.g. their search API - aren't open, as Mapzen's is(/was). Yet they are listed on that page by Mapzen as an alternative for Search.
There may be other such examples in that list.
Our data isn't, but as other commenters here have said, it's not currently possible to build a good geocoder with the open data available. We're constantly working to support open data efforts, but it's not there yet.
The geocoding engine[1] powering the Mapbox Search API is open source, and has been since its inception in 2012. The same is true of the routing engine[2] powering the Mapbox Directions API (OSRM), and the engine used to create Vector Tiles[3] for the Mapbox Maps API, along with the engines powering most Mapbox APIs.
Non-open code at Mapbox is usually tightly coupled to our infrastructure or data processing pipelines, which would not be generally useful to the community at large. The useful bits of even this infrastructure code is also typically abstracted into generally useful libraries for community use, such as earcut[4], rasterio[5], tile-cover[6], and hundreds of other modules of all varieties.
- [1] https://github.com/mapbox/carmen
- [2] https://github.com/project-osrm/osrm-backend
- [3] https://github.com/mapnik/mapnik
- [4] https://github.com/mapbox/earcut
- [5] https://github.com/mapbox/rasterio
- [6] https://github.com/mapbox/tile-cover