Why didn't aliens settle Earth before we existed?

i think aliens think like us, but are most likely more advanced than us...but maybe they have just discovered that our planet exists in this solar system and they want to explore it. i believe that one day we will meet aliens that come to our earth or that ren dez vous with us on the moon and all will be explained. many believe they are very intelligent creatures or that they dont exist, but i think they do exist. they are probably just discovering that earth has life on it