how

I mean, how in the sense than its any different than anything else? hierarchies exist almost everywhere.

Because miners physically compete to establish dominance over ledger writing authority. Worth noting physical power competition is highly egalitarian, noble, and virtuous. Especially when it's non-lethal like Bitcoin is.

Power-law actually

Hehe.. if you are concerned with the price denominated in clown world money... maybe. If you are concerned with how to ensure your permissionless and censorship resistant access to the network.. its all about real physical power.