Your body doesn't know the difference between hours sitting around meditating and hours sitting watching Netflix.  This story came up in the social hour after my meditation class last week. Per the American born monk who spent time in Thailand and gained - Imported Western junk foods are seen as higher status than traditional foods. Higher status food = greater spiritual benefits for the giver. In addition to unhealthy food around holidays they are even more sedentary to devote time to meditation and prayer. Work is to be done mindfully which frequently equates to slowly, so even something like handwashing robes in the river doesn't calorie burn like it would for someone who is just trying to get it done. Exercise is seen as attachment to the body, especially by older leadership without Western educations. It's not like it's just a Buddhist problem, I did  8 years of Catholic school, all the nuns were fat and all but the one youngest priest was fat. I can see how a life of sitting around praying could be really attractive to a fatty.