stockings' line

Over the past 6 years I have been purchasing Woolworths stockings(Shine Extra Sheer Stay-Ups) never minded the price tag because I always felt like it was worth it, but today to my shock the first fist pair after just wearing them once they treaded so I thought it was just my fault. Luckily I had bought two pairs this morning just tried the others to my shock they also just run (tore), I would like to know how that could come to be did the price rise & the quality of the product decline.