Perhaps because a lot of people with chronic pain issues or tissue/bone diseases/deformities are:

A. generally embarrassed about their condition because of feelings of lesser worth and uselessness and subsequently attempt to do as much themselves as possible

B. supposed to, even if it hurts them immensely, get a little bit of exercise in, even if it's only standing up once or twice a day

C. naturally more anxious or prone to introversion because of their condition and thus less likely to attempt to get someone's assistance