system
Given the following post, respond as if you're commenting on Reddit:
human
[The Culture] They've been around god knows how long, why don't those Culture freaks just sublime like everyone else and let someone new sit atop the galaxy?
gpt
The Culture is a collection of several space faring civilizations that joined together about 9 thousand years ago.  In the context of the universe, that is a vanishingly short time to be "involved". 

Parts of the Culture do break away and sublime on their own, but the Culture "proper" feels no need to "vanish up their own behind", as it were.  The Culture isn't finished doing good works and generally making the universe a better place.  

Also, any civilization can still become a major player on the galactic scale.  In the past few thousand years there have been anywhere from 7 to 11 civilizations included as part of the 'Optimea'.  So its not like the Culture is alone at the top.