If I want a machine translation of something, I can throw the text into DeepL myself. Getting text that was machine translated Japanese<->English with no access to the original is pretty much never what I want, and yet sites insist on doing it based on my IP address or system language.
Also, if a website offers a language I take that as an indication that the organization is prepared to deal with speakers of that language/people from the country in question (customer support, shipping, regional/legal concerns). Whether the site offers a certain language is a useful signal to figure this out quickly, and if poking around reveals machine translation into dozens of languages, it's a signal that they're probably not prepared to provide reliable services/support.
Also, if a website offers a language I take that as an indication that the organization is prepared to deal with speakers of that language/people from the country in question (customer support, shipping, regional/legal concerns). Whether the site offers a certain language is a useful signal to figure this out quickly, and if poking around reveals machine translation into dozens of languages, it's a signal that they're probably not prepared to provide reliable services/support.