It's strange how we haven't found any traces of life out there (aside from the possible Martian Mikes). There's, what? 100 billion stars out there? Surely not every member of every civilization out there just put themselves into the internet and lost all interest in space exploration?
I'm pretty sure that there is a perfectly logical explanation for the Fermi Paradox but we don't have the tools at our disposal at this point to figure out what that is.
Here's some ideas!
^^ About this one. As we know, there have been multiple human species throughout the last million years, some of them arguably as intelligent as we are. If the Neanderthals held up for just a few thousand more years, it's possible they could have eventually developed civilization. Maybe the denisovans as well. And some fossils suggest that there were multiple subspecies of Homo sapiens. Who knows what other humans we haven't found (like the one today). At one point about 500,000 to 1,000,000 years ago, there were as many as six human species living at once.
We're the only ones left. It's wholly possible that we're the Great Filter, not just as a species, but as a genus.
I mentioned that the Neanderthals possibly could have developed civilization. Here's a thought— what if they couldn't? What if there's some echelon of metacognitive processes necessary for a stable civilization to develop, that is nigh-impossible to evolve— and we did? Not only that, but we lived on. If we died out, then Earth-based life would have died out with our star.
Perhaps, on habitable planets that host life, it's somewhat common for an alien species (hominid or otherwise) to reach even a Neanderthal level of development (which by itself is an incredibly advanced achievement), but it's incredibly rare for the neurons to rewire themselves in order to make that last huge leap?
Perhaps that planet just isn't as lucky as ours and their star pumps too much radiation onto the surface, or a gamma-ray burst wipes out any chances at civilized life. Perhaps whatever factor that led to sapiens didn't exist or wasn't around in large enough numbers. Perhaps there was a predator that evolved to keep this lifeform down, either driving them to extinction or leading to a radically different evolutionary path away from sapience and towards something else entirely.
So when this species looked at the night sky, it never wondered what else was out there or why it existed. If it did, it could never make any logical guesses why.