We're talking about a proscribed health practice that results in continuing discomfort and sickness. Even if the benefit manifests as predicted, I'm skeptical it can make up for the low quality of life.
edit: I'm far from alone in this. When I share my aversion to sunlight, I find many more folks who feel similarly, than I do people who are puzzled by it.
I agree that strong sunlight on a hot day doesn't feel good.