One of my fellow Japan bloggers once remarked that her husband would not eat leftovers, so cooking was difficult as it required her to cook a fresh meal every night. In a pinch, he would eat leftovers if they were rolled into a new dish. My husband happily will eat the same meal two nights in a row, sometimes three, if I make a large quantity of something he especially enjoys. One of my friends has been known to make enough of the same dish for an entire week. I can't imagine eating tuna casserole for a week, but he'd prefer this to having to cook every night.
Americans in general don't love leftovers, but they tend to prefer them to the effort of daily cooking. Because of this, I thought my fellow blogger's husband sounded very spoiled in his refusal to eat leftovers, but I've come to learn since then that this isn't specific to her case. Most Japanese people do not favor leftovers.
I've asked quite a few people about this and their resistance to leftovers is multi-faceted. One reason is that they don't like to eat the same food two nights in a row. The emphasis on variety in meals is much higher in Japan than it is in the West. While we typically have three parts to every meal (protein, starch, vegetable), they often have five or more. Another reason is that freshness and food safety concerns are much greater in Japan. Japanese housewives often shop daily for the food they prepare for their family's evening meals. When there are leftovers, they tend to get folded into the next day's lunch rather than served as the next day's dinner.
Finally, I think the size of Japanese homes and appliances have a pretty big impact on a culture that hasn't embraced cooking for leftovers. In America, we often choose to cook more than we need, sometimes far more, in order to put some aside in the freezer for future quick meals. You can't really do that in Japan because freezer space is smaller as are most pantries.
I think that the Japanese way of handling food is actually very good. In particular, I think that the variety and freshness aspects are conducive to good health. On the other hand, it is a very labor intensive way of life. I can't imagine working full-time and doing the sort of work that Japanese women put into meal preparation. The acceptance of leftovers is, in part, an acceptance of a culture which says that women don't have the time to go shopping daily or to put efforts into what we might consider elaborate meals.