Why are long legs seen as beautiful?

Models all seem to have endlessly long legs. Women wear high heels to make their legs seem longer. On the other hand, in fashion, short-waistedness is seen as something to correct for (as is long-waistedness). So maybe the proper proportions are the most desirable thing?

When I’m walking around, though, I see women with short legs, and my aesthetic sense is less enthused by them than a woman with long legs. So which is better: short legs, long legs, or average length legs? Whatever your preference, why might we see this leg length as more beautiful than other leg lengths?