system
Given the following post, respond as if you're commenting on Reddit:
human
[DCU] Did Kryptonians ever rule the universe? If not, why?

They are conquerors and outside their planet they are super OP and have barely anyone to match their powers. Plus when Superman fights an enemy, the enemy recognises him as a Kryptonian. Does this mean that they were known for being extremely powerful? I just cannot understand why such an advanced civilization limited themselves to a planet when the whole universe was at their grasps. 
Also, with spaceships that advanced, why did they limit themselves to Krypton?
gpt
Once, the Kryptonians did in fact conquer and subjugate. 

But, the primary faith of Krypton worshipped their Sun as a god, Rao. Their religion held that the powers granted to them by other suns was thus unholy, demonic, and evil. They used the fact that it tempted them, corrupted them, as power inevitably does, as proof that their race was not meant to travel outside of the stars. When the religious caste rose to power, they shut down the Kryptonian space program, and created taboos about it so harsh, that centuries later the average Kryptonian still obeyed them, despite no longer being as religious.