I do believe the misconception is built upon a patriarchal foundation.

Perpetutators of patriarchy rely on rigid binaries to separate the "haves" from the "have-nots." One of those binaries, is, unfortunately:

Short Hair / Long Hair

...with short hair being symbolic of the authority and exceptionalism they wish to grant to men/boys, while longer hair is representative of the subservient position they want to assign to women/girls.

With hairstyles, this framework transcends gender or anatomy -- and it looks at whether or not a person is gender conforming in terms of their behavior/presentation.