I think there are a couple of reasons why stockings are so aluring to men.
Firstly, in the past, they were associated with somthing that was slightly risque, or outright sex orientated. Back in the early paert of the 20th century, stocking tops would never be seen, so if they were glimpsed then it meant that the chap had got way past 1st base!
The second reason is that they can make a womans legs look great. They cover any imperfections, dark colours will make legs look slimmer and longer and a.ccentuate the curve of the leg.
The promise of carnal pleasure if you are every lucky enough to reach what lies at the top is also a huge turn on for many men.