Why do we like dessert, but not extremely salty, sour, umami, or bitter foods alone? This is a "soft" question that's been bothering me for a while.

When cooking savory dishes, we usually try to balance out the five basic flavors (sweet, salty, sour, umami, and bitter) so that none of them dominates. None of these flavors should overwhelm the dish, but when present in the right ratios we will perceive a dish as tasting good.

On the other hand, we also enjoy dishes that are mostly sweet. In Western cultures these are eaten as dessert, usually after the savory portion of a meal, though in some other cultures (e.g. in Japan) sweet foods are traditionally eaten separately from savory meals. We do like having hints of the other four flavors in sweet dishes (e.g. salt in chocolate chip cookies, bitterness in coffee-flavored ice cream, etc.) but sweetness is certainly the dominating flavor.

My question is: why don't we have salty, sour, bitter, or umami equivalents of "dessert"? In other words, why do we not, for example, have a separate dish at meals which is overwhelmingly sour, which only a hint of the other flavors? Why is sweetness unique in this regard?
There's also probably a bit of biology involved: sugars are calorie-dense, and thus good sources of calories when you're struggling to survive on what you can forage. Bitter foods are often dangerous or poisonous in some ways; sour foods are often unripe, and thus harder to digest, and umami is a fairly neutral indicator. Salt can be dehydrating in large quantities. I have heard that this explains why little children need no coaxing to eat sweets but rarely like bitter or astringent foods.