Why do you think we are alone?
I can explain why I think we're alone... or virtually alone, in the sense there is probably no other "life as we know it" out there.
It's because our unique set of circumstances resulted in what we have. There are hundreds, if not thousands of variables which culminate in bringing about "life as we know it" on this planet.
What are the mathematical odds or probability that you could be sitting in Las Vegas and I could be in Atlantic City at poker tables and we would both be drawing the same exact hands at the same time, and this would repeat through thousands of hands? I would say that's a remarkably slim possibility... nearly impossible. Even if you had thousands or millions of people sitting at poker tables around the world, the probability that any two would be consistently drawing the same exact hands repeatedly is near impossible.
In order to have "life as we know it" anywhere else, there are so many circumstantial conditions that have to be met in precise order it makes it a near mathematical impossibility. It takes much more than simply having a rock in the Goldilocks Zone.
Now... microbial life? Plant life? Primitive forms of life? Yeah, that's possible.... but actual intelligent beings such as humans? That's a whole different ball of wax. For instance, you have to realize something.... Had there never been a mass extinction event that wiped out the dinosaurs, large mammals such as humans would've never existed here. We could have never evolved. So just that one circumstantial event changed the course of evolution and helped create "life as we know it" on Earth.
All land-based life emerged from our oceans... But life doesn't exist in a stagnant ocean. What enabled life in our oceans was the presence of a moon which caused tides and a wobbly rotation of the planet which created "seasons" on our planet and oceanic convection. So you're going to need to find another "water world" in the Goldilocks Zone, with a substantial moon close enough to create tides and the planet needs a wobbly rotation to cause seasons. That's just for the basic starter conditions of life to form. The course of that life's evolution will depend on thousands of other circumstances and variables, some of which are very delicate and important.