Most things are unhealthy because we eat too much of it. For example (fresh) bread is delicious, cheap, and healthy, provided you eat it in moderation. Now if you ate nothing but bread all day you would gain a lot of weight.

Same goes for salt, fat, and sugar. To be fair, part of the reason we tend to eat so much of it is because normally this stuff is rare in nature and we are evolved to seek it, but we’ve made it so accessible and cheap, that we easily let our natural instincts take over. So that aspect explains your trinity. But it doesn’t have to be that way. You can have all three with a bit of self control.