Serious question for evolutionists who believe in aliens

To anyone who believes in evolution and aliens, why do you assume that UFO’s must be “outer space beings” or “interplanetary travelers”? You already believe that humans arose spontaneously from the ingredients found on earth so why wouldn’t you also think that other beings found on earth also are from earth?

When I hear the theory that these “aliens” are actually from the oceans and that UFO’s have been spotted coming up from the oceans (or lakes in Alaska) that makes more sense to me. I don’t know if I believe either way but outer space creatures traveling millions of light years to hang out on earth is way less believable than complex intelligent beings living under water.

Scientifically, shouldn’t you use Occam’s razor? The simplest solution with the fewest assumptions?

We know there is life of earth. The “aliens” are found on earth. Why assume they are from anywhere other than earth?