Until about 30 years ago in Japan, foreign food was luxury food, even the humble sandwich. If you bought a sandwich in a restaurant, invariably it would arrive with the crusts cut off. It was more of an aesthetic affectation than a culinary decision, but it shaped the way Japanese people approached shoku pan (white bread). When bread became a staple in school lunches after the war, certain students, presumably the more well-to-do, would leave the crusts. Even today, if you buy a packaged sandwich in a convenience store, more likely than not it won't have crusts. And if you buy sliced bread in a supermarket or even in a bakery, the ends, or "heels," are not included, because it's assumed people don't want them.
Crusts and heels are categorized as pan no mimi (literally "bread ears"). Some bakeries just throw them in the garbage, but many sell them or even give them away. Homeless people frequent bakeries or bread factories to either ask for the discarded crusts or scrounge through trash bins for them. A lot of people use crusts to feed their pets or the birds that congregate in their gardens. As the recession grinds on and more and more middle-class folks are forced to cut corners, crusts have become more popular. Bakeries tend to have varied reactions to requests for discards, though.