How did it "die" in the late oughties, when FAIs were boasting about releasing routers with built-in NAS with torrent support in 2011, and projects like Popcorn Time only got popular in 2014 ?
A clueless gen-z user maybe, which was born with smartphones. On some media, ED2K and Nicotine+ (Soulseek network) it's the only way to fetch that content. Classical series/movies/comic books/special vinyl editions ripped into FLAC... those won't be at full FLAC/CBZ quality (high DPI png's) on YT/Spotify or whatever web site or APP for tablets.
I misphrased my first sentence. P2P's legal uses died with mobile. For example, Microsoft spent a huge amount of time and money removing the P2P functionality in Skype, because nobody was going to tolerate the data cost and battery drain of running a superpeer in your pocket.
Yes, people still use P2P for piracy. This is actually part of the problem, and why it was so easy for mobile to kill P2P. While P2P itself is legal, associations with piracy meant nobody was willing to use P2P, which meant nobody was going to invest the time or money into making mobile P2P work[0].
Tangent time: Have you ever wondered why we distribute online video through YouTube instead of BitTorrent? Remember, you could just put magnet links in RSS, there was even an RSS/BitTorrent combo client called Democracy[1] which was basically YouTube before YouTube. But a lot of corporate suits didn't want to touch BitTorrent in any capacity, even for things they intended to distribute for free, because of the piracy stink. YouTube was also ridden with piracy, but they cleaned up their act and brand with a bunch of automated moderation tools. So when online video became corporate, all the monetization and ads went to centralized platforms and not decentralized ones.
And as all of this should have tipped you off by now, I'm not a "clueless gen-z user born with smartphones". Even if I was, Zoomers figure out this shit anyway, despite Apple and Google's attempts to starve their brains of oxygen by denying them access to real computers.
[0] Yes, I know about AirDrop. AirDrop is just a taste of what we could have had if real engineering hours had gone into mobile P2P, instead of moving the few early adopters back onto centralized services.
[1] This would later be renamed to Miro and then abandoned as their YouTube API integration broke. Yes, they were also NewPipe before NewPipe.
Peertube can use P2P seeding just fine. Yes, I remember Miro. On 'piracy', that has no sense.
A corporation would just use P2P without even mentioning it, such as Wow did for online downloads.
Even Steam could do it to save up bandwidth.
And Activision-Blizzard eventually removed the peer-to-peer functionality from their update downloader.
I'm not sure why you are focusing so much on the mobile aspect though, most PC uses are still not done on a smartphone.
And what is possible changes over the years, even smartphones are massively faster than a decade ago.
I don't recommend that anyone distributes anything through YouTube (or any other platform) any more, and guess what, since a few years ago we now *actually* have a working YouTube (and more recently, Twitch) alternative !
And guess what, PeerTube is also P2P (based on WebTorrent) !
Just ignore these walled gardens, their enshittification is well under way anyway, and as long as you can show that alternatives are possible, you'll get enough users to flee them to greener pastures (see Xitter => Mastodon and Reddit => Lemmy as recent examples - though federated rather than p2p ones - I'm not a "decentralization maximalist"...).
P.S.: I've actually used Democracy Player / DTV / Miro for a while, but it was created (slightly) after YouTube, not before... anyway alternative YouTube players like NewPipe are missing the point - there's also the whole side of having to upload your own video through YouTube's shitty interface and random whims of their ContentID. And the whole ContentID extortion business goes away once the extortionists actually have to do the hard work of sending a full blown DMCA takedown, and then possibly have to fight in court against a fair use defense, and this whole thing becomes even more unlikely to work if your server is in a country that basically ignores those (consider how VLC violates DMCA because it's distributing libdvdcss, but they are pretty much untouchable because based in France - or also how MPEG doesn't bother going after the license violators that played a DVD with VLC without acquiring the license).
EDIT : heh, ninjaed about Blizzard and PeerTube...