When you don't know anything about linguistics: The plural of "memorandum" is "memoranda", why can't people get it right

When you know a lot about linguistics: Oh my god? So certain English words borrowed from Latin and Greek have competing plural forms, with one form using the English plural -s and the other using a borrowed Latin or Greek form? Do you realize how crazy that is - a language borrowing *inflectional morphology* from another language? And here the two competing plural forms have become markers of education, expertise, and social class, isn't that incredible?