The second wave of Gnutella and all of the various BitTorrent clients was decentralized. No single entity controlled the network so there was no single point of failure. Record companies and movie studios came after individual nodes, but were never ever to shut down the network.
However, no one ever invented a great way to do search and discovery on top of BitTorrent, so we've always had centralized servers for that piece.
It's not as convenient as something like napster or the like, but we've also got this draft <http://bittorrent.org/beps/bep_0051.html> to make it a bit better.
For anyone wanting to pursue this, I feel like I can share, I used this recently https://github.com/boramalper/magnetico, people share database dumps regularly. I found ~4 DB dumps and merging scripts are all you need to get up and running.
With links in centralized websites and fora we at least had a little more confidence on the safety/quality of the content.
To make decentralised search work you need to solve the trust problem. Strangers sharing content with you without spam, decoys, and malware. You need to create trust without any central coordinator. Crawling the DHT for content is not going to get you Google-quality search. The Tribler lab is working on the web-of-trust problem and decentralised (ledger) accounting since pre-Bitcoin days. Its a stubborn problem. But we're making consistent progress. Latest peer-reviewed science: https://www.ifaamas.org/Proceedings/aamas2021/pdfs/p1263.pdf
-Tribler teamYou can search bittorrent via DHT in a similar manner (I'm unsure if the bootstrap nodes there are strictly required) or search an indexer website from one IP then use the magnet link to download from another IP.