Given a pride of lions in Africa having severe domestic turmoil over leadership selection issues, what are the odds anyone in, for example, Wisconsin, either knows, cares, and is capable of sending an effective peacekeeping force?
You can even abstract out distance. I'm pretty sure there's some hierarchical struggle going on with the squirrels in my front yard, but I'm also pretty sure I don't care. And we're fellow mammals competing for the same nut trees and fruit bushes. If there are Star Trek Hortas tunneling under my backyard, I really don't care as long as they stay out of my basement.
Even within our own species there's a pretty strong taboo against colonialism that seems to automagically form right after (inevitable?) failed early experiments with colonialism. The odds of white people running Africa again are pretty low, even though we obviously did a better job than they are doing. Despite being incredibly easy to reach and staggering power imbalance, the colonies in Africa didn't last long and even a fairly irrational space alien would see the futility in trying to take over Earth.
There are many reasons to invade Canada. Stealing their resources of spar and mast grade timber for 1800s era sailing ships would be a pretty stupid idea in the current year. Its possible there's a natural magic filter such that being able to travel interstellar and having enough power to turn earth into a colony naturally means there are no material resources on earth worth the taking... What would a galaxy wide empire do with titanium, silicon based semiconductor electronics, or rocket engines, only miserable savages a million levels beneath them use stuff like that. It would be like handing a modern american a flint spear tip, what good is that other than in a museum?