I don't work at Twitch anymore so I can't answer your question without guessing and I rather not. There is always a likelihood that data gets used for reasons

I don't work at Twitch anymore so I can't answer your question without guessing and I rather not. There is always a likelihood that data gets used for reasons beyond the original purpose. In the best of world the hardware that runs on consumers devices would do the right thing which would allow the web to be a perfect sandbox. I think we're slowly getting there, in terms of video it's slowly getting to a point where H.264 support is "universally true" rather than a minefield although VP9 and AV1 is a bit of being back to square one. I think the spirit of my original comment was not to say "I promise that X company isn't doing Y" more to explain why this code existed in the first place. A search engine doesn't need to know what WebGL capabilities a device has as it doesn't deal with rendering whereas a site that has to work with hardware decoders most likely does need to know.