Seems rather like something out of the 19th century.
Indeed, but I bet that for every woman who genuinely wants to compete in a mixed category there will be a few who want a "women only" category. Just look at other walks of life: Womens' Institute, all the support networks for women, etc. It is everywhere.
Somebody must be into continuing this division pretty heavily otherwise it would not survive. I think a lot of women want to walk in their own non-patronising area and for example the good looking ones don't want to be accused of getting preferential treatment (which of course they would get, usually
).
And yes it is far easier for men to pee into a bottle (I should know; I am an expert by now, with flights up to 7hrs) but I gather the chemical (silica gel) alternative levels the field pretty well.