Why didn't Romans conquer/explore the African Atlantic Coast?

"Why didn't Romans conquer/explore the African Atlantic Coast?"

This question would make it appear that it is contemporary fact, that the Romans did not conquer/explore the African coast.

Roman sub-saharan Africa

Roman sub-saharan Africa

Between the first century BC and the fourth century AD, several expeditions and explorations to Lake Chad and western Africa were conducted by groups of military and commercial units of Romans who moved across the Sahara and into the interior of Africa and its coast. The primary motivation for the expeditions was to secure sources of gold and spices

The Romans also opened up trade and conducted maratime explorations.

Maratime explorations

Maratime explorations

The Roman vassal king Juba II organized successful trade from the area of Volubilis. Pliny the Elder, who was not only an author but also a military officer, drawing upon the accounts of Juba II, king of Mauretania in the first century AD. Pliny stated that a Roman expedition from Mauritania visited the islands of the archipelago of the Canaries and Madeira around 10 AD and found great ruins but no population, only dogs (the basis of the name the Canaries).

Therefore, the answer to "Why didn't Romans conquer/explore the African Atlantic Coast?", is "they did".

1. The Romans were pretty poor seafarers, compared to other Mediterranean societies.
2. The African coast is pretty much desert, until you go much further south than the Romans could possibly do - even if they were great seafarers. Note that Carthaginians and Egyptians did circumnavigate Africa, but those were single exploration journeys that took several years.
3. Their ships (as well as most other ships of the time) didn't have the range to cross that stretch of nearly uninhabited territory.
4. Whatever you could get down south you could get elsewhere for much less cost; it simply wasn't economically feasible.
5. Even if something (usually with hindsight) is technically possible, that doesn't automatically mean it happened. Thor Heyerdahl proved it was technically possible for Polynesians to visit/colonize South America. If it really happened is a very different story.

Because their ships weren't up to very long sea voyages, particularly if they didn't know where they were going.

The coast of northwest Africa is dangerous. The Portuguese called part of it the Cabo do Medo, which means the Cape of Fear. They didn't manage to get past that until the 15th century. The Romans were nothing like as sophisticated in terms of navigation.

You probably have a mental image of Renaissance-Europe ships, and of Ancient Roman ships. What's the difference? Well, a lot of things, but pertinently Roman ships needed oars as well as sails. On the other hand, Columbus and co didn't need oarsmen, and that's not because they were squeamish about slavery.

The Romans for the most part didn't expand because there was nice productive land they'd like to colonize. They expanded for political reasons.

For example, North West Africa was originally part of Carthage. After the Punic wars, the Romans simply gifted most of it to their allies/clients, the native Berber kings of Numidia and Mauretania. Both eventually picked the wrong side in one Roman political spat or other, and were absorbed directly into the empire.

There were no organized political entities further south to get fatally entangled in Roman politics this way. So any organized expansion into that area would have to be done by the natives themselves. The problem there is that the population of the Roman area reached it height not long after that (perhaps 160ish). From there on in Roman Civilization had a job on its hands just maintaining what it had.

Because the Sahara desert goes all the way to the Atlantic coast. The Romans were not great seafarers and required the support of coastal towns to cover long distances. The Western Sahara represents a break in that chain, over 1000 km of inhospitable coastline.

Even today, Western Sahara is one of the most sparsely populated areas in the world with an estimated 2.25 people per km². It gets 50mm of rain a year and is almost entirely desert. The climate might have been better back then (would love to see if there's research on that) but it never seems to have been particularly peachy. Western Sahara features no natural resources the Romans could exploit. The coastline faces no trading partners.

Along with asking "why not" we have to first ask "why". There's an implication in the question that the Romans expanded just to expand. No, they expanded with some purpose in mind. Spain featured rich natural resources. Advancing north pushed the barbarians back to give the Italian peninsula a buffer zone. Everything around the Mediterranean, including the North African coast, was interconnected by sea and coastal trade.

Even if they went all the way down to the better areas around the Senegal River, why would Rome want to spend the considerable effort to establish a city cut off from the rest of the empire?