It's because these sugar laden foods are not perceived as "bad." Would LovableLC's teacher given out vodka shots for the bingo cards? I think not!
It is very hard for a lot of people to believe that candy, cake, and cookies are dangerous. They will all agree that they are not "good for you," but at the same time they somehow don't agree that they are bad for you.
I think it's an inability to grasp a different conception of food that is different from the way they have always thought. Many times people ask what I've been doing, and I tell them, and they exclaim, "Oh, I couldn't live without bread!"
That's it, it's over, they can't even consider it, so their thinking stops there.