Ask HN: Why do we even have domain registrars at all?

It's probably a silly question I know, but given how much technology is open sourced and decentralised and whatever nowadays, why do we need to have ICANN and registrars and DNS servers any more? I mean, Let's Encrypt has basically destroyed the SSL certificate concept, so why can't there be something like that for domains? Or some system based on a blockchain or whatever, given I've seen solutions in the past where special domain extensions were set up in that? Why is this last part of the internet still commercialised and generally under central control?