It's probably a situation where everybody has his or her own unique set of circumstances that lead them to ignore (willfully or otherwise) established self-care and hygiene.

Decades ago, I worked with a man who seemingly had this or a similar issue. There literally aren't words to adequately describe how repulsive the scent was. It was a combination of not bathing, not wearing deodorant, dirty & musty work uniform, and like he must have some kind of medical condition / crisis going on with his digestive system because there was an undeniable fecal odor but it was orders of magnitude worse than just normal human poop smell.

In his case, I think it was a learned behavior (or lack of learning) / questionable upbringing. His mom was a pretty vile woman, just mean, spiteful, hateful, abhorrent. The manager would send this guy home any time he showed up smelling like he crapped himself. And every single time, she'd physically come down to the store to have a public showdown with the manager in front of customers and employees. So, clearly she was enabling the behavior and probably had been doing it for this guy's entire life.

I think the US has a large population of wolf children that nobody's ever bothered to study.

Dont put neurodivergent on that level