I think it's because it makes the legs look longer and therefore more attractive to men (with the exception of lesbians who might do it for other women, but these are a minority).
I think women look lovely in them but you'll be hard pressed to find a feminist wearing such things because it would be illogical...like you said, other than looking sexy, everything else is a negative. Feminists would never go out to look sexy because if men looked at them in that way, they'd slate them because they're doing what is biologically natural to them, yet the feminists were merely choosing the most efficient footwear for their mode of transport. 😠 How dare the man look at her in a sexual way...! 😋