A small offshoot of Philosophy hour.
I will refrain from writing the Internet's billionth exposition of the Fermi Paradox.
More interesting is the biologist's obvious answer: we - and other stuff like us - were never meant to cross the void ourselves. We're the fruiting body.
The Earth's biosphere has ripened, and reached the dispersion stage. To do so, it has developed a weird sacrificial outgrowth, a basidium known as "complex civilization" that can redirect all the resources of the organism toward a singular goal, propelling the seed outward. How? Space probes covered in microbes.
The seed must be low-maintenance, resilient, and apt to restart the whole cycle elsewhere - everything that humans are not. Who qualifies? The friggin tardigrades. We're just scheduled to make them nice little vessels, then die out quickly, lest we bring the rot with us.
There have been countless other civilizations, as short-lived as ours, including the one that sporulated in the general direction of our Earth in the first place. They went through apoptosis before they could come here in person - and we're obviously all the better for it.