I believe if life is common than there must of been at least one group of aliens that at least attempted to colonize it self everywhere in space?
Unless humans are a extreme anomaly and that most other aliens don’t really care about space exploration, and just focus on their home planet.
Also, it's very easy to imagine a kind of planet on which intelligent, advanced life could form but which is significantly more difficult to leave than Earth. If you're on a planet with even slightly stronger gravity and thicker atmosphere than ours ... good luck. It won't be easy.