That's another, related thing. Unlike modern day where you can dye your head purple and slouch around with your gunt hanging out, PCs in RPGs are typically in a line of work where their bodies are their primary asset. Even the wizard in the back is traveling long distances in rough terrain, sleeping in caves, carrying all their shit on their back, etc, and unless they're magically levitating themselves and their stuff everywhere, they're probably getting far more exercise than an easy 80% of modern people in industrialized countries. If you can't carry your food and supplies while walking twenty miles a day in a fantasy setting, you have a significant problem. Your average adventurer is probably skinny with muscles like piano wires, no flabbos and definitely no non-functional limbs. People who are not strong and healthy can't even get from point A to point B in a fantasy world, much less feed themselves off the land and still be in shape to fight for their lives day or night.