Most bald men don't have a completely hairless head, they keep the chaplet (not sure this is the right word, but the dictionary says it is) for a very long time. Understandably, Patrick Stewart didn't want to actually grow his hair out enough for it to show. Either way, if you want to look like Picard you usually need to shave your head every couple of days even if the top of your head is completely hairlesss, and it's annoying to do it yourself - if you have a skillful barber in walking distance and can afford his prices, you'd go there all the time. And the barber is usually happy, because it's easy money.
Thank you for coming to my "ruining the meme by taking it seriously" talk.