The universe is way too big for this stupid little planet full of xenophobes to be the only sentient life out there.
They probably have seen how we treat ourselves and our planet and saying, "Yeah, there's no fucking way we are helping those assholes out."
I like to think (Without investing any belief) that they saw the way we broadcast our xenophobia. If you put yourself in their, well they probably don't have shoes as such, but place. The metamessage for the past 83 years has been "Come to Earth, we'll kick your ass!" You'd think that the planet that invented marketing could come up with more than one statement to the universe at large.
Looking at that, The War of the Worlds through Independence Day: Resurgence, I'd be willing to bet that if they do come here, it'll be armed. Not to swing by Old Man Otis' cabin, and make "Beep Beep" noises with deelie boppers on their heads.
We challenged the universe to an Invasion. Don't be surprised when they do show up, ready for a fight. After all, we're literally asking for it.