Oh, I agree with you. I don't really understand why sites don't use language headers which obviously specify the user's preference. I've never been on the implementation side for sites that were clients - I just explained the tech, showed how they could use it, and then they used it in those ways and many times more. Maybe it was just easy rather than having to use multiple variables? Maybe they don't know about this header (which would be shocking IMO)? But back in 1999/2000 time frame, no site was using the language header which may or may not have existed back then - I honestly don't know when that was introduced into browsers (I was a Netscape Navigator user back in those days).
I'll also say that even though I invented IP location technology, I am an avid user of privacy-shielding VPNs. Just because you invent something doesn't mean you don't regret some of the uses of said thing.