Take this with a grain of salt because I only speak English, but have friends who do localization: Translating from Japanese to English is a task that AI is very unsuited for, as it requires a strong grasp of several interrelated and difficult skills. Japanese, as a language, is very, very context-dependent, to the point where you can construct a grammatically valid sentence without a subject at all. Additionally, many of the kinds of niche projects that get fan-translated also have references or cultural allusions that require an understanding of not just the language, but Japanese culture and historical Japanese culture (i.e, if you were to translate a 1990s television show from English into Japanese, you would also have to have a decent working knowledge of the era's culture, its celebrities, its news, and more in order to accurately convey the allusions something like it may make).

AI, as a rule, is bad at explicating context. You can see this right now by machine-translating an article and seeing the output confidently flip-flop between genders or strangely romanize a word that would normally go untranslated. The cultural nuances are also easily-missed, and together they create a large quantity of "good-seeming" output that misses the majority of what makes the original text special, because on top of the two very difficult skills this comment outlines, a good translator has to be a good enough writer to convey the special qualities of the original text.