Fewer remember modified mp4 with patched atom location to help play media while downloading off a CDN.
For most mobile users, using the more modern VP9 and HEVC essentially just burns battery life, and even modern GPU based desktop users usually see their card warm up on YT.
MP4 is far from perfect, but play/resume/skip-to location media mods for a web-server are common (js or html5 support is stable.) This saves a lot of grief setting up media servers, but most people now just use an online platform... rather than figure this stuff out.
I kind of miss the days a lazy layman coudn't post lame garbage video content.