Many a mother has to insist that her children eat the crusts of their sandwiches. And that's with the soft (though somewhat rubbery) crust of American sandwich bread. A lot of European breads have crusts that would defeat a child's teeth.
When they grow up, the children may develop a taste for that crunchy crust, with all the browned flavors it gets from being directly exposed to the heat of the bread oven. But the child's delight in the soft, spongy crumb of bread lives on. For many people, the true sign of a fancy buffet is the crusts that have been cut off the finger sandwiches.
This taste for crumb goes back at least as far as the Renaissance and the Middle Ages. In those days, poor people mostly ate a heavy rye bread and only the well-off could afford a light, high-wheat bread called manchet in England. To get it as high as possible, bakers made sure to bake at a high temperature.
As a result, the bread had a very tough crust, which had to be chipped off with knives before the luxurious, spongy crumb could be served. The crust chippings didn't go to waste--they were sold or given to the poor, who thickened their soups with them.