The formerly decentralized services are no longer so decentralized since "free of charge, paid for by data and ads" has shown itself to be a viable business model that users love. (Until they understand what's happening, at least.)
People keep saying this but to my knowledge email still isn't centralized. While there are a lot of gmail users in the US but that's not the case in many other countries, many people also have a .edu email and a few years ago I ran my email server myself (I even handled signing papers when I switched jobs over it.) Google even contributed to and pushed for dkim and spf which solved a huge spam problem that threatened their ability to forward mail from smaller outside domains to their users. A lot of people might use one of the big services but as long as you don't have to in order to interact with them it's not "centralized."
There is no control within Facebook's ecosystem. Similar with AOL, if you don't use Facebook, you're necessarily out of the loop, and I don't feel comfortable with that.
Not to detract from your point, just thought you might be interested to know that USPS actually has a legally-protected partial monopoly on the right to carry letters (18 U.S. Code § 1696).
An exemption was added in 1979 allowing private carriers to deliver "extremely urgent" mail. This is why UPS and FedEx express mail envelopes bear that text on their front.
Apart from this exemption, USPS, FedEx and the like are only allowed to deliver 'parcels', not 'letters', though I'm not sure where the distinction is legally defined.
More info: https://en.wikipedia.org/wiki/Private_Express_Statutes
But it is absolutely federated - I have the choice of running my own server and can communicate with every other e-mail address on this planet.
Unfortunately, it isn't easy to setup - average Joe has no chance to get his own server. On the other hand, for IT people it isn't extremely hard either. Once setup, it is nearly maintenance free...
I'm running my (and a company) e-mail server since 2001 and I don't want to miss it. I only once had a problem with being blocked by big sites, after moving to a new server where the IP range has gotten on some blacklists, because of the previous owner. Also never a problem with spam filters.
I hope e-mail will never be replaced - or at least there's some new way of communicating federated where every internet user is reachable.
This is what happens as technology progresses. I don't think the solution here is to abandon imperfect technology in favor of old, but to improve upon it.
If we need e-mails and phone numbers to sign up for social media, then we don't actually need the social media. We can go back to simply using the numbers and e-mails.
Better to extract the value of Facebook and move forward by eliminating the negative, than revert to something many people find less convenient.
I disagree that we currently do. And only agree for email in 1998 when its decentralized nature costed more to the users than the benefit of being decentralized, hence the transition.
Nowadays, any kid can get online. The range of intelligence and character has expanded dramatically.