So while waiting at the bus stop on campus I did some quick counting, and about 40% (plus or minus about 15%) of the women wore tight leggings. (The next day was substantially colder and more windy; then it was more like 15%.)
I hear that it is necessary to suffer to be beautiful, or at least to get attention. If my undershorts get stuck that far from battery I look around for a place to inconspicuously adjust the uncomfortable situation. Those have to chafe.
Claiming that leggings cover more than other forms of clothing is disingenuous: they reveal the shapes precisely and without any even the visual boundaries that swimsuits give. As part of a series of layers no doubt they help keep one warm, but by themselves? Worn with callipygous intent.