When Columbus and other explorers were exploring, profit was a factor. There was the potential for immediate financial gain. It didn't require Trillions of dollars spent over several years in R & D.
Comparing exploration of the Americas to exploration of Mars is like comparing apples and oranges.
I don't agree. There is just as much "potential" for immediate financial gain today as there was then. And it doesn't require "Trillions of dollars spent over several years" today, either -- the key word being require. Consider the dinky boats they launched then, they couldn't haul much cargo back. But they wanted spices or other rare goods of high value. It is perfectly feasible for us to go into space after rare items. But the initial cost is prohibitive for corporations. If you look back in history, private corporations were not funding the initial ventures, and when they got into the game they were given monopolies.
I bet if a corporation was created owned by IBM, Intel, General Motors, Texaco, and Procter & Gamble; and this corporation was then granted complete economic and total economic rights to both the moon and the asteroid belt, and the US government guaranteed to protect that right militarily (think East India Company and Great Britain) that suddenly the economic exploitation of space might get a kick start. The East India Company was very tied to the Empire, and was a major factor in permitting the Empire to exist at all.