Well, still, for a company that tries to make everything "simple and beautiful", why don't their video streams just work everywhere out of the box? That is the question.
What Apple's live streaming does, is in a CDN friendly way dynamically adjust the bandwidth going to a stream consumer. It's a great invention and there's no reason other people haven't adopted it. It's not being proprietary, it's simply being smart, because it's not trivial to do this kind of broadcast on the internet.
Here's the reality of video, and this goes for a lot of things that Apple makes "simple and beautiful". They fundamentally aren't. Video is a fundamentally difficult mess, a PITA, and the only way to have it work really smoothly is to have enough control over the entire stack to ensure that things work they way they are supposed to... and even then it doesn't always work. People adopting MP4 as a standard has gone a long way towards making things "just work" generally, but it's not sufficient by itself for a quality live stream.
I remember trying to watch a previous live stream from south america and the difficulties I had, even though I was using Apple devices and software the whole way.
Simple and Beautiful is a contradiction from "everywhere out of the box".
Those are two opposite goals.
This is an important thing to understand about software broadly, but with video it borders on impossible.
The thing is that any cable company in the US and Canada that streams content to their customers via the Internet is using adaptive bitrate streaming either using HTTP Live Streaming, MPEG DASH, HTTP Dynamic Streaming, or Microsoft Smooth Streaming.
It is far from impossible.
Everything is simple and beautiful if you are already embedded in the ecosystem/walled garden. If you are an outsider, it is another matter... Isn't it more or less the goal of every tech giant ?
Apple fans can justify anything - so don't expect anyone to say, yeah they are behind the curve on this.
The better answer is probably: "They simply don't care". No ifs and buts. Probably making it a bit exclusive and hard to get to only adheres to their marketing philosophy.
