I've got a better theory. Interstellar civilizations have probably fought wars over habitable planets and in the aftermath of those wars they probably have set up some rules for a long time about what you're allowed to do on habitable planets in a galactic framework. In fact, the reason this planet is not strip-mined and every living thing on it dead thousands of years ago is they probably have some rights in there given to life that evolved on a planet.
Besides, E.Ts can probably do ok in deep space or underground on lifeless planets if they can do interstellar travel.
Besides, E.Ts can probably do ok in deep space or underground on lifeless planets if they can do interstellar travel.