They figure the hair just sort of grows without much effort. It just shows how little they understand us. For men, growing facial hair is a significant achievement. All other honours pale in comparison. Sure, facial hair will grow if left unattended, but the true beard experience requires us to look in the mirror every half an hour and rub it thoughtfully.
Some men have it easy.
There were guys in my grade seven class who had to shave twice a day. At twelve years old Billy Reardon looked like one of the Smith Brothers. The men in my family have never been known for their body hair. I suppose we've found better uses for our hormones. Being blond on top of everything else adds up to not much on my upper lip.