What if Earth is like one of those uncontacted tribes in South America, like the whole Galaxy knows we're here but they've agreed not to contact us until we figure it out for ourselves?
Everyone jumps to the most wonderous conclusion possible when it comes alien life, but this in my opinion is the most plausible likelihood. Humanity is not only a relatively new civilization, but it would also kind of make sense that in the grand scheme of things we aren't really all that important as a species. We only just reached our own moon less than 100 years ago. I think the idea of humanity being just a mediocre species in the grand scheme of things is scarier thought to some people over the idea that we are of some unique importance.
It would also make sense given that lots of "official" declassified reports of UAP/UFOs tend to focus around nuclear and military testing sites as well as active war zones. Kind of like they are checking to make sure we aren't annihilating ourselves. I can just imagine an alien civilization laughing over the fact those stupid hairless apes got into another war and being informed in sheer horror that not only did we split the atom, we used it as a weapon against our own kind just to see what would happen instead of using it as an energy source.
So, if you really want to go down that rabbit hole, how about this;
-All life desires to stay alive.
-There is no way to know if other lifeforms can or will destroy you if given a chance.
-Lacking assurances, the safest option for any species is to annihilate other life forms before they have a chance to do the same.
Source;
Dark Forest Theory
I've wondered something like this in the past. It's a super interesting theory. Especially the more you think about it. There could be a huge intergalactic society out there. But then again, we'd probably have observed something by now.
Capitalism. It leads us to selfdestruct. Therefore, only civilizations that managed to overcome that obstacle managed to reach spaceflight, and they are watching us right now in shock and horror as we dance towards the planetary obliteration fully aware of what we do but unable to stop because few thousands people's profits are more important than entire species.
Well, it's as good answer as at least few other Fermi Paradox answers.