I never found Fermi's paradox, or rather, its argument, to be particularly persuasive. Or perhaps more accurately, I do not think it means we ought to be surprised by the fact that we have not heard from anyone. There are still plenty of unknown factors concerning how hard it would be for species capable of interstellar travel to evolve (and how long they would last), and those who feel confident galactic civilisations should exist seem to have filled these gaps in our knowledge with optimistic assessments (or should I say "assumptions").
Several possible answers are presented in
the Wikipedia article on the subject, and most of them seem at least plausible. It could be pretty much any of them, or a combination of several.
The most tragic solution to the paradox is that intelligent life wipes itself out (or, somewhat less grim, knocks itself back to an earlier stage technologically) before attaining interstellar travel. Or, various types of astronomic or natural disasters could do it. However, one does not have to go there.
It may not be possible (within physics) to develop technology for travel to the closest habitable planet (we don't know how frequent they might be) in less than several generations. It may cost incredible amounts of resources to make such trips, far more than it would save from the planet of origin in less than incredibly long term, which would make it an act of incredible altruism for whoever financed it. Indeed, it may even be an act of incredible altruism to embark on a journey into the unknown, never to see home again (and for your children and grandchildren to spend their entire lives on a space ship) for the possible benefit of civilisations of future generations. It may be beneficial for the survival of a species to not have all eggs in one basket as in all living in one place, but that doesn't mean it is beneficial for the individual. And evolution is about survival, ultimately on an individual level.
It could be something along the lines of Star Trek's prime directive, or them avoiding us for some other reason, such as that we are not interesting to a species capable of interstellar travel, frankly being animals to them.
There are plenty pf more possibilities tat can hardly be ruled out. And again, it could be almost any combination, with thecumulative effect of making galactic civilisation highly unlikely. Just a couple of them in unison should make galactic civilisation unlikely enough.
We may never know what the actual explanation (or combination of explanations) is, but with so many possibilities, I see no reason to be surprised we have heard nothing.
