> because aristocrats and monarchs don't seek power in most systems;

This… well, I’d urge you to read some English history. I’m choosing English because it’s the one I know best.

It is a litany of power struggles, of brother and sister plotting to kill aunt, uncle and father, nephew cousin, niece and anybody else. Of factionalism in court, bloody takeovers and power struggles. Noble houses vying for position as the monarch’s favoured ones, taking land and riches from less favoured houses, or winning it back. Scions of noble houses at war with each other over succession. Monarchs slaughtering potential usurpers. 9 day monarchies as one successor is positioned against another when the old king died, all based on religious backing…

There were long periods of stability under certain monarchs too, but often these coincide with periods of extrinsic conflict. Sometimes their wars of adventure would come close to bankrupting the country. Other times their choice of who to marry (or divorce) would cause massive loss of life.

They very much select for the power hungry, the venal, the egotistical and those capable of subterfuge and great violence to their own blood.