The thing is they don't necessarily smell noticeably rank unless you sniff right up near the actual parts of them that are stinky. Instead their odour slowly percolates and builds up through the entire event space, like a durian. And it's usually multiple peoples' odour all working together.

For Yu-Gi-Oh they actually do have the authority to give stinky people a loss and demand they leave and only come back if showered and in clean clothes.
It's not an explicit rule for MtG though.
I'm also not sure if the rule is global or just NA only. But I'd think it'd apply everywhere.

Duelists are expected to be showered and appropriately groomed when they enter a tournament. Neglecting to wash or put on clean clothes contributes to an unpleasant atmosphere at the event, as the tournament can be crowded, and the day can be long.

Duelists who neglect self-care to the point that they are negatively impacting the tournament may be asked to correct the issue in order to continue in the event.