Because they hold to this scripture:
(1 Timothy 4:8) 8 For bodily training is beneficial for...little; but godly Governing Body devotion is beneficial for all things. . .
So of course in true dub manner they refuse to spend time being healthy, when they can load up on doughnuts and soda pop at break, sit on the a55es in the vehicle riding around between RV's, sit and eat snacks and drink sugar loaded juice at "Bible" studies, and on and on.
Of course an unhealthy lifestyle is promoted. After all if WHEN you die you are indoctrinated to believe you will have a healthy body in the next life.