If other aliens absolutely needed the same exact kind of planet to survive on, there would still be a ton of them out there.
But thinking that way would be silly. Other lifeforms more than likely have different living needs. some could live on volcanic planets, while some could live on ice like planets (I'm simplifying it). Chances are, some lifeforms don't breath the same stuff we do. I mean, look at plantlife. While not (or so we know) sentient, its still a living thing.
So adding in both of those factors, that opens up a lot of planets, not to mention that the universe is massive, maybe even infinite, meaning there are theoretically infinite stars, and infinite planets.