Personally, I find that incredibly depressing. I mean, these are women who've chosen a social media site that only lets them reveal 140 characters of their soul, and they can't even show you everything on the outside? It's just a bad idea for attracting men. It's kind of like guys trying to impress women with cock pics that are just close-ups of their pee-hole.
"Hmm, that is one promising urethra. Well, in for a penny, in for a pound, I guess."
It's harder for guys to get away with this, with the possible exception of close-ups of beards, and even that has limited appeal -- specifically to ladies who get a special feeling from stabby follicles, but in a good way. Also, nine out of 10 of guys posting close-up beard pics are covering fatness or compensating for baldness.
Take-away Message: This is as good as I get. Everything else I can show you will be a bitter disappointment.