system
A chat on subreddit /r/me_irl
human
MLA is the standard for English studies, which is why English teachers use MLA. Sorry that your other teachers never taught you their domain-specific citation style, no matter how many times English teachers have repeatedly begged them to do so.

Source: am an English teacher.
gpt
Probably more of a factor that we arent writing research papers in high school that require the APA.