Why is called a 'manhunt' when they know the target is a woman?

It is hard to find the origins but I suspect because in the past men did the hunting so men were selected to hunt for the criminal or missing person regardless of sex.
The “man” in hunt was describing the people mostly males that were rounded up not the person that they were searching for.

Because man meant mankind, or humankind. Plus, men are usually being hunted anyway, they are more likely to be the violent criminals.

Perhaps “man” refers to the hunters.

I think @JLeslie has it right. “Man” in the sense of “human”, not specifically “male”. As opposed to a cathunt or a doghunt. Like you wouldn’t call the search for a female dog a “bitch hunt”. :)

The ”-man” in “woman” doesn’t mean “male”, it means “human”. A lot of complaints about sexism reveal a lack of linguistic knowledge.

Convention.
The same reason coppers and military officers demand to be addressed as “sir”, despite NONE of them having ever been knighted by the Queen of England.

It comes from “human”, and as far as I understand it, it is the hunt for a criminal/fugitive, not the hunt for them, by a group of people.

Also, manhole.

It’s as @rebbel and @JLeslie says. Also for simplicity of language. For example, you could say redheadwearingbluedressinblackheelswithleatherpurseinblacksportscarhunt.

Too many syllables…