Decentralized communication absolutely works, and we have plenty of decentralized tools now. Decentralized search is a legitimately hard problem, both because it needs strong protocols (which are getting there but still WIP) and user adoption (which isn't really happening).
That’s not the reason email has re-centralized. It’s because big-tech companies provide it for free in order to bind users to their services, and at least in the case of Google, also to collect data and drive ads.
As someone who administrates their own email server and works at an SMB who administrates their own email servers, it works quite well and doesn’t require centralization.
"When mice march with elephants it's in the mices best interest to be cautious"
I've done a lot of a lot of email administration over the years, servers with 100,000s of accounts, and you walk a very fine line in being able to communicate with the rest of the world. Your IPs must exist in certain blocks (or at least not be in banned blocks). You must block outgoing spam messages at a much higher rate and quality than google/hotmail do. Get yourself blacklisted for any reason and expect to disappear from the internet, meanwhile no one is going to block the largest services.
Mail servers aren't real people or real businesses.
50 year old decentralized protocol has problems, so decentralized protocols can't possible work. Just like 50 year old computer can't play doom, so doom doesn't exist.
Search systems aren't real people or real businesses either. Never mind details like how you define and enforce "real" in a decentralized way across N legal systems with wildly varying ideas of what it means to be a "legitimate" business. There is no system or ledger you can query to find out if a given person is real or a business is legitimate. This is exceptionally unlikely to change on a useful timescale.
The basic problem with email is that it assumed good-faith participation from the parties involved. It was assumed that only legitimate actors would have the resources to participate and they would always be well-behaved. This, it turns out, was flawed on several counts. For one, it assumed legitimacy could be assured. For another, it assumed legitimate users would be well-behaved and would never abuse services for gain. For a third, it assumed account takeovers or other impersonation attacks wouldn't happen.
Every de-centralized system that aspires to not have email's problems needs to take them seriously.
Decentralized communications may work, but decentralized internet search is probably always going to be impractical.
The actual logic involved in search is itself pretty simple and almost trivial to shard, the problem is dealing with a mutable dataset that is of the order of a hundred terabytes.
Search gets enormous benefits from data locality, such that distributed approaches are all significantly more expensive.
