Do you think aliens in ufos have visited Earth? (And all things UFO)

New to this thread. I was just wondering, if somebody could explain to me, why aliens would leave their home in time to travel hundreds of light years to arrive now, when for the vast majority of this planet's 4.6M history it had nothing but pond scum, and a mere 100,000 years ago the most advanced life forms (besides the mice and dolphins) were apes barely able to light a fire?