I think many of those systems were created by elites who dominated the use of violence and fed off the work of the subordinate classes. Their use of violence was a skill that was crucial for them to learn to be good at but only had to be used intermittently, so they had a relatively large amount of free time to spend on governing and thinking.

This explanation is only partial, of course.

I literally told you that it was technology - agricultural revolution in this case. This made people specialised so that they dind't have to waste time slogging for food which freed their mind up for other mental activities.