Standby for a spot of armchair psychology.
What is sexually desirable is an interesting example of nature / nurture. There are some aspects that are hardwired, some that are picked up totally from learned experiences and (probably most) are a combination of the two. Sexual identity (straight, gay, bi etc.) is hardwired and you don't get a say in it. Being a foot fetishist or into bondage is probably more towards the nurture / learned response end of the spectrum.
Stockings etc. are a cultural thing and likely to be a conditioned reponse. My guess would be:
Stocking were originally functional - women wore them because they made legs look better or were part of uniforms.
'Forbidden' things automatically become attractive. Since blokes weren't meant to see women only wearing stockings, getting a woman to the stage where you saw her wearing just stockings meant you were almost certainly getting your leg over. Ergo, stockings = sex.
Once that has happened, seeing other women in stockings automatically becomes arousing as it triggers that association and you think "I might get to stick my cock in her".
That becomes a standard cultural viewpoint and from then on younger lads discovering they like girls find that sexual pictures = stockings and that link is perpetuated.
Similar associations happen in different cultures, the standard example being really fat women in some tribes. Being fat = having lots of food = rich. Given multiple generations being fat becomes aspirational for the girls and sexually attractive for the boys (and ScaleyAlbereto obviously). Tits are sexualised in Western countries as they are hidden away and 'forbidden', therefore getting your grubby little mitts on them is a big deal. In cultures where women walk about topless all the time it's not sexual.
Are you suggesting that stockings originally were worn to cover hairy legs? That reinforces my preference for silky smooth female legs. I thought that breasts were sexualised because of their role in feeding babies? Big boobs being equated with well fed nippers.