That it, right?

Some people want 480p video.

Some people want 1080p video.

Some people want 4k video.

Even if the browser <video> tag did a great job at codec and resolution negotiation you still have to encode _at a minimum_ three copies of the video to hit the qualities. Multiply that each time you need a different codec for different devices.

Or, upload one video to Youtube.

And target device specific playback resolution also comes for free from YouTube. So it will not be 4k on mobile. But it could be.

That doesn't mean people don't want to serve 4K video.

It means they want the video to be encoded in multiple resolutions for different levels of connection. Another thing that's not necessarily trivial, especially at scale.

I wasn't talking about consumption, I was talking about the people making the videos. They do not want people to watch it in 480p unless it's the last resort. It's a similar mindset to famous directors hating when people watch their movies on phones.

I've fought and lost this battle many many times, and have used mobile bandwidth as a reason too.

High resolution video hosting/streaming is free, so no one wants to pay to host it. I think there are major downsides to hosting on YouTube, but in my experience the vast majority of people do not care.

Thankfully YouTube gives you different qualities depending on screen size and network speed, without you having to recode the video a dozen times. And for free. ;)