It's illogical from any point of view.
Some aspects of it are, some aren't.
I mean I can understand Krypton itself being like... the golden city that no one REALLY wants to leave unless it is their duty or job and the more villainous Kryptonians really can't settle for anything less. There aren't too many Americans flying out to 'uncivilized' parts of the world to kill their population and take claim of them for their own gain (and I mean... living there). But why aren't there diplomats? Deep space scientists? anthropologists?
I mean they are described as scientists and they cured every disease and ailment ever afflicted on them... So it isn't like they need any medical scientists anymore.
People do go out and exploit the boonies however. That's how the countries both of us are living in got started. And clearly with Krypton tech + superpowers the boonies wouldn't stay boonies for very long. Presumably Kryptonians live a LONG time too, and the race should be frikkin ancient, so this just should have happened. The fact is they only exist as a thin premise for where Superman came from and why there aren't any more.
Yeah if they could. But I'll put it like this Reelya
Kyptons are so advanced that as long as they are on Kypton they have a magic box. If they want it they can reach inside and pull it out with absolutely no effort.
There is no materials, labor, devices, or anything they need from anyone else. They want for nothing. If they want power, they only want power for the satisfaction of lording it over others.
The Shuttle Superman came in... is the equivalent of a rocket ship someone built in their garage and it is still one of the most advanced spaceships in the known galaxy.