Simple (VERY simple) life will likely turn out to be quite abundant in the universe, and even in our galaxy. Our ability to tell if an exoplanet supports very basic microscopic life (the form our planet's life existed in for the rather large majority of time that there was any life at all here) is very limited. We're not even certain about some satellites of our gas giant neighbors in our own solar system. The exoplanets orbiting other stars that have been identified as being to some degree candidates for life are all basically right in our galactic back yard, and we can't "see" them well enough to tell if they even have macro-sized life, to say nothing of the much-more-probable microscopic critters. We've looked at only an infinitesimal sliver of our universe so far...and will probably not expand that sliver all that much before our species goes extinct (even if that takes millions of years). Space is that big...

The only way our "window" significantly expands is if an extraterrestrial species evolves technology and starts sending emissions outward at lightspeed: radio signals, and suchlike. Depending on both signal strength and the sophistication of our detectors, that would expand our "window" enormously...but still probably not realistically beyond our own galaxy (one of literally trillions). Our galaxy has a diameter of about 100,000 light years. We're not on the extreme edge, but for simplicity's sake, let's say that 100k light years represents the furthest we could detect an artificial signal from (although we can't even come close to that for any signal we could produce, even something like nuclear detonations). We've only had the ability to detect (or send) such signals even in a crude manner for a little over a century. And even the next-nearest galaxy would be way beyond the distance from which we could detect a civilization that was anything less than a Kardashev Type III. The signal from anything lesser would become far too dispersed before it got anywhere near us.

So any alien civilization we'd have a chance of knowing about would have to have hit the stage of generating detectable signals within the last 100,000 years. 100k years is an eyeblink in terms of astronomical time. There could have been literally millions of such civilizations in our galaxy alone, existing sequentially w/o overlap, that went extinct before we got to the point of being able to detect their emissions. Unless we eventually stumble across their remains out there (a massive longshot...), we'll never know they existed.

That's what I mean by life being "brief." How long do technology-using species last? We have no idea...but our own species isn't at all old (in an astronomical sense), and we've already hit the point where we could kill ourselves off, to say nothing of things like comet and asteroid strikes, nearby supernovae, lethal plagues, and so forth. Space is big...and so is time. It could very well turn out that we'll never be a combination of near enough and near-simultaneous enough to any form of extraterrestrial life or even evidence of its remains to know if we're not alone.