Memes

Ships, including ocean-going ships, were a thing long before 15th century. Europeans have travelled to North America in the 10th century. What happened around the 15th century was the creation of empires willing and able to colonize (plunder, steal, enslave) on a continental scale. The idea that the amerikas were somehow "the new world" rather than land stolen by massacring natives is imperialist propaganda. I think this is the reason why a lot of people fell for "colonize mars" bullshit - they subconsciously think that the land now occupied by the US was a barren wasteland which couldn't support human life until brave europeans came and covered it in McMansions and fast food chains. From that mindset it makes sense that we can do the same again, but with mars.