"Misogyny" didn't start out as a word meaning the systemic oppression of women. It was a cognate to "misanthropy", the hatred of people.
As it happens, women are systemically oppressed, which led people to redefine "misogyny" as meaning systemic oppression of women. This was honestly a terrible idea. We have plenty of words describing the systemic oppression of women, such as patriarchy. And many patriarchal sexists don't hate women; they're just incredibly wrong about what is good for women. There's also bad stuff that's done to women by people who don't hate them and think they are being egalitarian, except that women and men aren't starting from the same baseline in our society, so treating them exactly the same where "exactly the same" means treat them all like men runs into serious problems.
I have been fighting for the word "misandry" and pushing back against this nonsensical "misogyny means the systematic hatred of women" nonsense for 15 years, now, and I never saw the "misogyny must be systemic to be misogyny" concept until people started trying to declare misandry a non-word. I feel that in fact misogyny got redefined precisely so that radfems could delegitimize misandry.
Imagine a boy is raised on a feminist commune with way too much radfem input, and they tell him that women should be in charge of everything because men are naturally violent, and women are better at social interaction, that's just a fact, and he should just accept that he will never be allowed to be in charge of anything. If he begins to hate and resent the women who are given more privilege than him in the local society that he doesn't know how to leave, how would we describe that except misogyny? This hypothetical boy doesn't know that, outside the commune, men run the world, because the information he's allowed to have is heavily censored. He's not hating women because he has a sense of entitlement and wants to dominate; he's hating women because they're oppressing him. Cool motive, still misogyny. It doesn't actually mean systemic oppression of women, it means hating women, full stop. There is so much hatred of women in the systemic oppression of women, it's easy to confuse the two, but they don't mean the same thing.
No one is systemically oppressing humanity, yet the word "misanthropy" for hatred of humans exists. Misanthropes are equally likely to particularly hate the powerful as they are to particularly hate the oppressed. In fact, a lot of misanthropy imputes the behavior of the powerful to "all humans" as a justification for hating us all. Since misanthropy comes from other humans, and not from, say, sentient walruses who hate us for causing global warming, it cannot be re-imagined to mean "systemic oppression"... and it is where the word misogyny comes from. Someone went back to the Greek roots that make "misanthropy" and reconstructed them to make "hatred of women" instead of "hatred of people".
I feel that misandry is an important word and we shouldn't let it go. Anti-masculism sounds like hatred of masculinity, which is probably a very valuable word in its own right, and not exactly the same thing as hatred of men. (Among other things, the anti-masculist would dislike butch women and would have no problems with femme men, if it meant hatred of masculinity rather than hatred of men.) I'm convinced that the campaign against misandry originates from the radfems, and that's why feminists now believe "misogyny" has to mean a systemic oppression. But there's nothing in the roots of the word to imply such a thing, and it's not very useful to take a word with a specific meaning and then make it mean something else we already had a word for.