It just depends on the phase every single hair was going through before being waxed. A few hairs were about to fall off, so at the end of their cycle, those will be the first to grow back, beacause a new hair is about to be developed. So the sudden hair reduction is only apparent, because simply the earlier on their cycle and/or the shorter the individual hair was before being waxed the later it will grow back. They grow back as layers. Then, you probably wax another time that first stray regrowth, when they are long enough. This time the first layer of hair growing back will be denser, they are just the following layer already about to grow back. You will be confused and think "Damn it i just waxed, and what's more they are even denser than the first time!". You redo, and finally this time they are less. You may so reconsider just shaving your legs and thighs like many women do, at least you don't suffer and don't have to wait them to grow back long.