What is the point of colonizing on Mars?

people say the sun will engulf the earth in about 75 million years..wont mars go with it? i mean i know the world will get over populated and we should go there but wouldnt you go some where else out of the solar system, where there is another sun? then again we are going to need that sun + earthlike planet +atmosphere/water/oxygen+close to us(distance) combo..