Exceptions that prove the rule. Out of thousands of cultures, the number of premodern societies that attempted any serious, sustained exploration can be counted on one hand. And really, its doubtful that premodern migrations to the Americas were any kind of deliberate exploration effort. It was probably just nomads following the herds.
Look at this way, modern humans have been around for about a quarter of a million years. The first migrations out of Africa were only about 30,000 years ago. If exploration were really some fundamental human constant, it seems odd that we spent 90% of our time in a relatively small portion of one continent.
Actually, proto-humans migrated repeatedly out of Africa. Homo erectus, Homo antecessor, Homo neanderthalensis, and finally two waves of Homo sapiens moved out of Africa and into Eurasia. North America was colonized repeatedly by Homo sapiens, by the Amerindian, Navajo-Dene, and Inuit peoples. Migration probably is in the genes. Lineages that become widespread are harder to wipe out as a result of drought, famine, climate change, etc. so lineages with some innate tendency to disperse probably tend to survive. But it's kind of a moot point. The places they went to already had atmospheres, normal gravity, ambient temperatures, radiation shielding, abundant game and edible plants. Mars has none of that. It was simple enough to move out of Africa that a cave-man could do it, literally. It doesn't follow that because humans could and did repeatedly move from continent to continent that it's a good idea to try to colonize a cold, barren, airless wasteland millions of miles away.