Kryptonians had some reason for not being explorers…maybe their moon blowing up. But they had a specific reason for not already having spacecraft…hence Jorel having to build a rocket. I would think they would try and save the planet rather than escape.
Also i believe in Byrnes version there was no Jorel trying to convince people. He discovered what was happening and the crisis was almost immediatly upon them.
The moon was blown up by Jax-Ur. The deeds of one evil individual would not deter them from space flight. Maybe with Krypton’s higher gravity spaceflight was highly impractical absent a life-or-death scenario. Here in the Sol system, I think that the most likely scenario would be that the Kryptonians would terraform and colonize Mars. A weekend project for a few hundred of them, I’d think. Then when Brainiac came, he and his ship would be no match for the sheer numbers and all of a sudden they have a complete city.