Totally unscientific theory: sweeteners are to sugar what methadone is to heroin. If you're using them, you're still craving/addicted to sugar and your palate remains out of whack, so you're probably also drawn to sugary foods that don't use sweeteners (eg. most commercial pasta sauce, ketchup, fruit juice, many breads).
> ...users consumed lower amounts of fructose and higher amounts of caffeine than non-users, but had similar diet quality.