Anubis is a community-made map by a guy called jd40. This is the second map to be featured in CS:GO active duty map pool by the community.
To become a new map that CS:GO will take seriously, the map needs to have technical certifications that work well in order to become a competitive map in the Active map pool. The new maps have to be polished to the point where the visuals and the technical aspects are. For example, all players need to be visible close to any surface of the map, in order to become visual correctly. Over the years, maps have got more and more optimized to a point that the game runs smoother.
If you are one of the Anubis doubters, go what this impressive video from Olaftw, where he explains every technical detail about the map.