Earlier quoted context omitted.
You know why you don't see systems like this at any scale Because they don't work.
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).
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.