Presumably, the original spaceport was built at a location that made sense relative to the points of interest on the planet. The craters, radiation, and other such aren't going to disappear just because you stopped bombarding. Especially after a saturation bombardment which covers a wide area. The disruption represents the effects of bombardment, not that it's ongoing.
But that's all an in-fiction explanation and isn't terribly important. Gameplay-wise, it seems like it'd be more or less ok either way, but I like the idea of not being able to just bombard the hell out of something and re-colonize it like nothing happened. Have to at least wait for the glass to stop being liquid after you glass the planet, you know?
