I know that the Romans when they were on their empire's peak around the 1st and 2nd century AD, controlled the northern coast of Africa and had the Sahara desert as some kind of natural "wall" as well as border of which they thought that it is the end of the world so they did not bother to explore it.
But looking at this map, I do not understand why they did not expanded further west from Mauritania Tingitana. In Roman times, this coast was pretty fertile as was rest of northern Mauritania and Numidia. So why didn't they expand further west on the North African Atlantic coast? As far as I know, thanks to their old enemy Carthage, they knew that there was a lot of land in that direction since Hanno traveled down to Gambia centuries ago.
I mean, the Romans were expanding everywhere they could. And since the African Atlantic Coast was not really claimed by any empire or strong barbarian hordes in that time, there was no resistance against the Romans.