The fact that we exist as carbon based life forms makes it somewhat likely other life forms exist. We're made of the most common elements, whose signatures we observe in other stars. But in order to exist, we needed time for first and second generation stars to create heavier elements. So, space is only part of the limitation, time may be the more key reason we don't hear alien contact.

This is pretty similar to what is described in Stanisław Lem's "The New Cosmogony" (a work of fiction, included in the book "A Perfect Vacuum"). Only there the terrarium-like isolation of intelligent species is a self-imposed restriction: The earliest civilisations of the cosmos engineered the laws of physics that way.

It's a really common theme actually, almost a trope in sci fi.

That's some serious security by isolation, not even Qubes OS comes close.

In time, as the expansion of the universe accelerates fast enough, not even light will keep up to get across.

Perfect total airgap.

Perception of time is relative. Not the universe's fault we live like mayflies.

Seems a little inconvenient for the architect to have to account for all the laws of physics and allocate millions of cubic light years of space just for our tiny rock when they could just squish those of us that escape, or at least discover the true nature of our environment, like we would ants on a kitchen work top.

Ants don't have a pernicious ability to build progressively better technology in an attempt to escape the kitchen work top and conquer the refrigerator. Or, rather, they do, in the sense that they are life and life has this tendency, at least in the one case study we have access to.

I don't know, I like to gently brush them into a dustpan and dump them back into their anthill.

I can't explain why, but ants are some of my favourite animals.

What do you think happens to those ants, sir? Coming back with tales of being brought up in a flash of light, anally probed, seeing mosquitoes spontaneously exploded, giant ships transporting them to earth.. socially ostracized, is what. Made fun of on the front page of Ant Times.

Speed of Light does a pretty good job of creating a natural bubble. An advanced galactic society may have the knowledge and tech to detect patterns in solar systems that may produce life in the future and predict which star systems may have life.

Is humanity even generating enough radio signals that may be even remotely possible to detect on Alpha Centauri (4.367 light years away)?

What better way to study an intelligent species behaviour that to put it in a dense rich easily traversed environment it could spread through and populate, generating lots of data.

We are the control group

Totally original and excellent thought but just have to throw it out there... Three Body Problem... Liu Cixin is trying to tell us something...