i think "inquest" would be a more appropriate word for the thread title than "autopsy"
a phenomenon that is multi-determined in its genesis will have multiple causal strands involved in its de-genesis - and all that have been mentioned so far contributed to its fading away
but if there was a single pulse that you could track as the life-line, the vital sign, i'd argue that it's the vibrancy and the essential role of the pirates
there is something about real-time terrestrial broadcast to a geographically restricted audience that creates community and a sense of synchronisation - everyone within the same forward-surging temporality
as soon as it became about the internet and netradio, you are leaving behind analogue culture - you are into geographically scattered audiences whose identity is primarily through identification with genre (whereas with jungle, UKG, grime et al - the identity came from the genre-identification but also a host of social and racial factors).
you are also into desynchronisation - the ability to listen to shows when you feel like, when it's convenient, as podcasts or archived shows
this is just my experience, but living in NYC and then in LA i could never bring myself to listen to netradio of nuum-type music - it just felt wrong - i was listening too far away from the source, and at the wrong time of day
i think hardcore continuum is fundamentally an analogue-era culture - you can see that with the way it stuck with vinyl and with the dubplate long after other kinds of music had abandoned those for digital modes (there were still really shitty-sounding bassline 12 inches you could buy in 2008 - a phenomenon of persistence completely different from the vinyl revival going on elsewhere, which was the musical equivalent of artisanal cheese - almost literally, given that you could buy 40 dollar vinyl albums in Whole Foods here)
also feel like the broadcast nature of pirates contributed to a certain (delusional?) grandiosity - the DJs and MCs could actually say and feel, "this one goes out to the London massive" or whatever - the music is addressed to a whole city and its population (in potential, at least) - a lot more people were aware of the pirates than actually liked them (indeed they found them a nuisance)
in that sense it was a public culture
internet is narrowcast