There's so many different thoughts to this.

1.) Earth is in a really special location in that it's a nice distance from the sun, it has a number of much larger planets protecting it with their gravities and the solar system isn't too close to the middle of the Millky Way to be too radioactive. It's in such a perfect location for life that it might be hard to replicate.

2.) There are so many planets circuling so many stars in so many galaxies and life could take so many different forms that it seems mathematically impossible that Earth is the only planet capable of maintaining life. The water on earth didn't come from Earth, it came from the ice on asteroids, so there's definitely water/ice out in the universe...