Tentative theory: the Puritan (or possibly Protestant work ethic) thing never went away, but at some point it got mated with gaining status through self-expression, and with gaining status through your clothes getting to seem too easy, which is why people shifted to high-maintenance bodies.. That's why running ultramarathons on multiple continents seems cool rather than weird and extravagant.

This isn't about philosophy, exactly, though you may be able to deduce a plausible philosophy to explain what people are doing. It's about cultural shifts.