Genderspacing this particular tag would also lead to every other tag needing seperate genders if you operate logically, and that is an extreme amount of work for little to no payoff. In some cases it would even just lead to confusion for example in gender / body swap stories. Would you tag a male teacher swapping bodies with his female student as male:teacher and female:schoolgirl uniform or the other way around? And that's just one example.
No one has the necessary time or insanity to actually go through 30k+ galleries and check each and every one of them for what gender a tag should be categorized under if we changed it to that system, and in the end almost no one benefits from it since most of the tags already are exclusive to either females or males and for the most important ones where gender actually makes a difference we already have seperate tags like Rape and Reverse Rape. Even if we just changed the glasses tag to be gender specific we would have to check thousands of doujins for it.