system
Given the following post, respond as if you're commenting on Reddit:
human
[DC] What exactly kept the Kryptonians from conquering galaxies?

If we assume Superman is an average Kryptonian, it seems they could have simply charged up their soldiers near a yellow sun, and proceed to stomp reality. Why did they not do this?
gpt
Kryptonians are xenophobic by nature, and had their own problems to deal with. They were focused more on perfecting their own bodies and minds, and on perfecting their own world.

They came close to this, but it came at a cost. Births were strictly controlled. Kryptonans were nearly immortal, with cloned replacement parts always at the ready. A person's place in society was decided for them by their house and their caste and their religion. Social mobility was almost non-existent.

Kryptonians worshipped their star Rao as a lifegiving force of light and life. They considered themselves the guardians of their world and their lifestyle. They felt entitled to their decadent lifestyles.

A civil war broke out between those who believed that clones should have rights, and those who felt they were merely "blank templates" incapable of living without the machinery. This left Krypton's surface scarred and barren, and took much work to rebuild.

In the meantime, two key events related to space exploration took place. There was a period where Kryptonians were willing to explore the stars. Not much is known about these initials explorations, except that the Kryptonians were mostly ruthless to other races they encountered. Many of these explorers were secretly sabotaged by a weapon from the wars known as the Eradicator, so most exploratory missions ended in failure. 

However one group chose to be more friendly, and founded the Daxamites, who created a more peaceful and open-minded culture, which endured for quite some time.

The second key event, the key to locking them to their homeworld, was the destruction of one of their moons by an ill-fated attempt to interact with a meteor. Space travel was banned outright, they'd gotten little benefit from it anyway, and had much to do at home.