Customers purchase this because they want to avoid any pinching that a waistband might create.
Waistband-free hosiery is hosiery that has no waistband.
It has a nice panty portion that helps to hold up the legs of the hosiery. The panty portion is made by creating an extra long piece of fabric, and then folding it in half, inwards, and then sewing the raw edge to the joining of the legs and panty portion. It might be simpler to think of the panty portion as a normal sized panty that is made of 2 layers.
This is sometimes called,