Since men are normally assumed to wear their hair short, this tag shouldn't be used for male characters. An exception to this rule is made for particularly feminine males, as they are often depicted with traditionally female hairstyles.
This is something like how loli and child are different tags because loli is explicitly used to denote explicit content with underaged characters (which also locks it off from regular users) - the tag is used for the purpose of looking for a specific type of thing (women with short hair), and suddenly putting nearly all the images of men on Danbooru into the tag will make it nearly useless for searching, as well as be a giant headache to actually retag everything. Sure, "short_haired_woman" might be more accurate, but I'm not sure it causes enough confusion to be worth changing all the tags and forcing people to write out longer tags.