lack of regulations* allow, and no not exactly;
eu and canada have stringent laws on advertising to children, and laws on nutrition and additives to their products
even things like bread in the US have an insane amount of sugar
but the other reason is suburban/car culture & zoning, which means more hypermarkets and shopping not every few days for fresh food but every week or two for more processed food that lasts longer because going to the store is a bigger PITA than a quick 5 min walk to the neighborhood stores; which also means mroe walking rather than driving, another area of calorie burning and lean muscle maintenance which maintains high metab
Why is the quality of food in Europe so much worse than southeast Asia?
Because you guys are way, way, way fatter than e.g. the Japanese.
Back on topic -- we have excellent food in the US, but regulations allow for highly processed crap to be sold too. Pretty sure most of the crappy processed foods are easily available in Europe, too.