Why do websites now prefer IP-based geolocation rather than the Accept-Language HTTP header?

As an avid VPN user it’s infuriating that multilingual websites insist on using the client’s IP address to determine their language and country when web browsers have been sending the Accept-Language HTTP header since the mid-90s.

I understand that you can work out more or less where someone is located based on their IP address but it was never meant to be a geo-based marker. Why not go the simple route and use the header?