• Fermi famously asked "Where are they?" referring to the fact that we haven't heard from any alien civilization but statistics shows that we should have
• The explanation could be simple: sentient life lasts a very short time wherever it happens.
• The evolution of life follows roughly the same pattern on every planet where it can arise. An asteroid may wipe out the dominant life form and cause a regression, but fundamentally life follows a predetermined course towards more and more sentient species.
• Unfortunately, sentient species become capable of building powerful devices, including devices of mass destruction, and eventually will use them, wiping out their own species.
• Unfortunately, sentient species become less and less interested in reproducing (fertility drops as they become wealthier, life expectancy increases, and that combination translates into an aging population that cannot take care of itself)
• Unfortunately, sentient species create rapid technological and economic growth that destroys the natural environment that these beings need in order to survive. "Intelligent" beings are beings that destroy and kill: kill other animals and destroy forests and rivers. Their intelligence yields technology that kills and destroys. The atomic bomb destroys in one second, but widespread industrial and consumer technology destroys on a much bigger scale if at a slower pace.
• The advanced stage of a sentient species (the stage when the sentient species has developed the technology to communicate with the other sentient species of the cosmos) lasts only a very short time before the species self-destructs. It probably coincides with the stage of self-destruction: if a sentient race has developed the technology to communicating to other planets, most likely it has also developed the technology that will destroy itself.
• Therefore the window of opportunity is very small. Our messages may indeed be received by their devices, but the chances that they are still alive to read those messages is very low.
• Ditto for us: we will probably have self-destroyed when our planet receives messages sent by aliens.
• Everywhere life can happen it has evolved roughly like on Earth, from brainless forms of life towards more and more sophisticated brains.
• Unfortunately, sophisticated brains are doomed to invent roughly the same technologies, including the technologies of mass destruction and the technologies of climate change, and are doomed to settle into a non-survival mode.
• A fundamental law of sentient beings makes them self-destroy.
• It is inevitable that more and more sentient beings arise, it is inevitable that they invent more and more technologies, it is inevitable that they wealthy, it is inevitable that eventually the products of their intelligence cause their extinction, and possibly the extinction of all life on their planet.
• We are just a program that repeats itself all over the universe, wherever life can arise: life arises spontaneously, then it spontaneously evolves towards sentient beings, which then naturally start building technology, and inevitably they also develop the technology that can destroy them, and then inevitably this happens. And all of this happens in exponential time.

See also The Human Race is Genetically Programmed for Self-destruction .