could someone please explain to me why morbidly obese people smell sour?
You're not going to like this so hold onto your lunch (or breakfast or whatever) but basically it's a problem with the folds of flesh.
Because of them it's really difficult for really grossly fat people to get properly clean, so they're usually carrying around a fair bit of rotting gunk in odd crevices of their bodies.
And that kind of makes some of their skin start to rot a bit aswell.
.................... I did warn you.......