Why does it seem many women's formal clothes require the necktab?

So I've noticed this when my friend posted a picture of her and a couple buddies in their dress blues (USMC). The women all had a necktab thing, I had to google the term, with their shirts showing more and the guys had the regular collared jackets where the shirt was barely visible. I ended up looking at Army and Navys formal clothes and saw the same thing.

Just wanted to know if anyone knew why it was like that. In my honest opinion, I personally prefer the way the mens looks and can't see any functional reason why the womens looks different, other than a desire to tell them apart. Which also makes little sense to me given you wear the same uniform regardless, the only difference being acceptable hair lengths.

So trying not to sound disrespectful and rude, but just curious on why there's a different jacket (excuse my ignorance if that's the wrong term btw) for men and women. And lets say, for whatever reason, a female wants to wear the mens jacket instead. Is that possible or does she have to wear the females one?

Again, really not trying to sound rude but my curiosity got the best of me and I can't figure out why when I Googled it, other than reading about (for reasons I can't decipher) some guys angry responses to Marines shifting towards a mens style jacket for women.