I use a few platforms, including airbnb, when I look for accomodation. What makes airbnb better? The only different thing I noticed is that they validate my ID.
Of course the obvious answer is network effect, but I guess you're saying that's negligible here? I think I agree. I also think that a decentralized version, which can more easily avoid censorship, will deliver more value.
Is there a decentralized anything that has been successful outside of email?
Generally not unless there is an actual need for the decentralization. Otherwise it's easier and more profitable to build a centralized platform. BitTorrent is a decentralized success because there is an actual requirement that it is decentralized.
DNS, although the individual registries are each centralized.
The great Dyn attack of 2016 would disagree with you in practice.
oops i guess not in terms of having a website. but it _feels_ totally different— like a distributed community— than all these top down financially motivated “sharing” economies.