Mayan Civilization - A different approach

December 21, 2012 is over and we are still alive in this world, which proved wrong that world will end. Let me first make it clear, whatever I have given here is my view and not to harm anyone's belief.

Mars Colony (80000): Private spaceflight company, SpaceX is targeting a huge Mars colony of 80000 people. CEO, Elon Musk confirmed this on his talks about Mars Settlement Program, which will start with 10 people first, costing $500,000 per person for a trip. "At Mars, you can start a self-sustaining civilization and grow it into something really big," Musk told an audience at the Royal Aeronautical Society in London.

Assuming this 80000 count is reached and people start new civilization in Mars, say after 50-100 year. Why not extraterrestrial creatures, assuming they are advanced developed in technology like us, dont think of migrating to earth. If some extraterrestrial elements found Earth to be opt for their living and migrated some thousands and thousands of years ago and had their own civilization? Why not Mayan civilization is one such well advanced civilization? Why not someone from their generation launched similar Earth sharing process ? Why not this Mayan civilization come down to earth and settled for years before they disappeared suddenly ?