Younger folks forget that YouTube launched (2005) a few years before both the iPhone launched and Netflix pivoted to streaming (2007).
In that weird era, (a) average home Internet connections became fast enough to support streaming video (with a healthy adoption growth rate), (b) the most widely deployed home recording device was likely still the VCR (digitizing analog video from cable to burn to DVD was a pain), (c) there was no "on demand" anything, as most media flowed over centrally-programmed cable or broadcast subscriptions, and (d) people capturing video on mobile devices was rare (first gen iPhone couldn't) but obviously a future growth area.
So early YouTube was literally unlike anything that came before -- watch a thing you want, whenever you want.
That was also an era where bandwidth to serve content was extremely expensive, I still don't know how 2005 YouTube was able to find a way to make serving user-uploaded videos for free financially viable, but that was a HUGE component of their success.
Also, the DMCA had just passed, which basically eliminated liability for hosting copyrighted video content as long as the infringement was laundered through a service provider.
I honestly don’t think YouTube would exist without that particular piece of regulatory capture.
Contrast the video and podcast ecosystems.
Podcasts are arguably much healthier (the publishers maintain creative control), and are certainly decentralized.
I think the secret was being acquired by Google. Without the deep financial pockets and strategic patience of Google, I doubt they would have been able to become what they are today.
At YouTube scale, it feels like that quip: 'When you need to serve a few videos, it's your problem. When you need to serve video everyone watches, it's the ISPs' problem.'
On-demand was a thing before, but it was mediated through slow, glitchy cable and satellite boxes. There was also a thriving scene of RSS-delivered web TV shows.
Really most of the content that YouTube had available was material recorded off of broadcast/cable which was mostly not available otherwise unless you had recorded it or gotten it off a torrent.
In that weird era, (a) average home Internet connections became fast enough to support streaming video (with a healthy adoption growth rate), (b) the most widely deployed home recording device was likely still the VCR (digitizing analog video from cable to burn to DVD was a pain), (c) there was no "on demand" anything, as most media flowed over centrally-programmed cable or broadcast subscriptions, and (d) people capturing video on mobile devices was rare (first gen iPhone couldn't) but obviously a future growth area.
So early YouTube was literally unlike anything that came before -- watch a thing you want, whenever you want.