This isn't really about centralization. It's about federation. And as much as HNers may want it, nobody else does. Let me introduce use to the Plain Old Telephone System ("POTS"). POTS is a federated system. It's true it's also open addressing, which is a factor but not as much as you might think.

People hate POTS. You're identified by a number. It includes a (now meaningless) area code. Portability is a problem. You can switch carriers (although prepaid portability can still be an issue) but it's a process. Also, whatever portability you have disappears when you cross a border.

POTS is filled with spam. Just like email (another federated service). As soon as something is federated it becomes incredibly difficult to police bad actors. If you, as a telephone exchange has too much spam (eg robocall) traffic, you might find yourself blacklisted by large players like Verizon and AT&T. So what do you do? You "launder" such traffic with enough legitimate traffic so as to not trigger any enforcement while charging extra for known offenders. Because that is profit.

A federated system is inherently a game of whack-a-mole with bad actors while being a race to the bottom.

Messaging services like Twitter, FB (Messenger) and WhatsApp all grew and continue to exist because of centralization while federated alternatives inevitably always die or simply never gain real traction. There are real efficiency issues. For example, when policing offensive material (eg CSAM) is each entity responsible? How is that efficient? They might have to do because given material may never leave a given node.

The question you should always ask is: what problem does this solve for the user that they care about?