i'm still of my own theory, that is shared by some that these "aliens" are actually ancient humans who fled a long forgotten surface war and fled underground........just look around the globe, there are a bunch of civilizations that used to live underground for a while for unknown reasons, military complexes are built underground.
What if its just a different strand of humans ??
"so how is the things on surface,scout?"
"they are still dumb and toss their garbage where their food income is"
"oh well, maybe another day we will share our enlightment with them"
"if they dont kill themselves first"
"or that"