system
Given the following post, respond as if you're commenting on Reddit:
human
[Superman] Its often shown that Superman's parents knew he would have powers on Earth. If they knew about yellow sun light, why didn't they just shine this kind of light on themselves (or any kryptonian)?

It seems like with a whole planet of supermen, an exploding star would be a minor threat...

Also I think I remember synthetic yellow light giving superman powers.  Why couldn't kryponians on krypton do this? 

And if it had to be starlight, why wouldn't more kryptonians just leave the planet?  If there was a city on the other side of the country that would give me god like powers for just being there I would go there immediately. They seem to have the ability for intersteller travel.
gpt
Their planet was under a red sun. It would take more than just "shining light from a yellow sun" on themselves to overcome the red sun's effects.

As for why they stayed on Krypton, that varies from continuity to continuity. The big thing that has stayed the same since pretty the very introduction of Krypton as Superman's homeworld is that no one believed Jor-El that Krypton would be destroyed.