Mine is probably the most boring: There are many intelligent species in the universe. Faster-than-light travel, however, really is simply impossible, meaning that there cannot exist a truly interstellar civilization. So while some species have probably settled solar systems other than their own through generation ships, suspended animation, time dilation, or whatever, their range of expansion is limited. This means that encounters between species of different planets are rare. Humans will most likely never contact any intelligent alien species, at most one or two. We might, however, discover evidence of their existence through telescopes or something.
Part of the problem could be current technology. We blast radio waves into the ether, but those radio waves degrade over distance. Any radio we put out will be just background noise by the time it reaches an advanced alien civilization. It could be radio isn't even the dominant form of communication, so that's why we aren't receiving any kind of space chatter.
I wouldn't say that the Fermi Paradox is nonsensical. It's based on theories of habitable planets, age of the universe, and similar technological advancement in habitable planets. I agree there must be alien life out there, but it is strange to not see any clear signs yet. The galaxy is mapped, stars/planets move in an orderly fashion. Something very large moving in a way that doesn't make sense with it's gravitational orbit should be a clear sign of alien life. Hasn't happened.
Now why an alien species would make a dinner plate the size of a planet and attach thrusters to it is another question, but even so, you'd expect to see something.