You didn’t know, because it started with Gloria Steinem in the 70s.

Wikipedia tries to make it sound like it’s some old tradition, but it’s actually fairly new, with the prior historical references being obscure until it was resurrected. It’s right there in the article:

> “Ms. was another acceptable, but rarely used, abbreviation for Mistress in England in the 17th and 18th centuries.[12] During the 19th century, however, Mrs. and Miss came to be associated almost exclusively with marital status,[13] and Ms. was popularized as an alternative in the late 20th century“

https://en.wikipedia.org/wiki/Ms.