There are probably hundreds of potential solutions to the Fermi Paradox, the puzzle, first mooted by Enrico Fermi, that, there is a discrepancy between the lack of conclusive evidence of  advanced extra-terrestrial life and the likelihood of its existence.

Without challenging the fundamental logic of the paradox itself, there seems to me to be one abiding factor that makes it likely that we will never meet up with those hypothetical aliens. The universe is so vast - our galaxy alone is mind-boggling big - and the speed limit is so constrained by the laws of physics, that no advanced civilisation would bother to want to get much beyond their solar system.

The speed of light is that limit and getting anywhere near it is well-nigh impossible. There are serious problems with trying to travel that fast, including the infinite amounts of energy required and the strong possibility of colliding with even the tiniest particle, lethal at those velocities.

Currently Voyager 1, which travelling at quite a clip, would take over 70,000 years to reach our nearest solar neighbour, Proxima Centauri, a mere 4 light years distant. Aliens may choose to invest in long-term robotic colonisation via self-replicating spacecraft (see von Neumann probes) but even then, what is the return and why do it?

Why not settle for exploring the local solar system, with perhaps a robotic foray or two to the nearest star system? I think this is probably why we will never meet ET, though there does remain the possibility of detecting life at a distance, as we are now doing with SETI.