Actually you do have to stay in shape you could get a heart attack from the stress(160+ beats per min for heart rate) chess causes especially in blitz otb cause you still burn thousands of calories in chess so it does require physical exertion just in A very very different way from the norm
If you have high blood pressure or have diabetes or something like that your at risk of getting a heart attack in the middle of game so fit=important
I don't really think it's about logic when physical ability isn't the focus and is clearly defined