The main reason is simple: many Japanese homes, especially in large cities, are compact.
In a typical urban apartment, the available floor space has to be divided among the living room, bedrooms, bathroom, storage, and everything else a household needs. The kitchen is only one part of the home, so it often receives less space. This does not mean Japanese people rarely cook, and it does not mean they believe a small kitchen is better than a large one.
What makes these kitchens work is the amount of thought that has gone into using limited space well. Many Japanese appliances are designed to be compact without sacrificing performance. Rice cookers, microwave ovens, refrigerators, toaster ovens, and other everyday appliances are made to fit smaller homes while still being reliable and convenient. Kitchen manufacturers and homebuilders have also spent decades refining the placement of sinks, stoves, cabinets, drawers, and storage so that as little space as possible is wasted.
Generations of designers, manufacturers, and home cooks have learned how to make these kitchens function under tight conditions. The result is not simply a collection of appliances squeezed into a small corner. It is a space planned around short movements and easy access.
Because of that, a Japanese kitchen can feel more practical than it first appears. The sink, stove, refrigerator, and storage are usually close together. You do not have to walk across a large room every time you need an ingredient, a pan, or a plate. Once you actually cook in one, the short distance between everything can make cooking much more manageable in practice.
The way people cook has also adapted to the space. In many homes, cooks do not spread every ingredient and utensil across a large counter before starting. They take out what they need, cut it, move it to a plate or bowl, and then reuse the same small work area. Used tools may be rinsed or put away while the meal is still being prepared. This partly comes from having limited counter space, but it has been normal for so long that many Japanese people do not think of it as a special technique.
Of course, small kitchens still have real disadvantages. People who cook often may feel there is not enough room for a cutting board, several bowls, or ingredients for more than one dish. Storage can also become difficult when a household owns many plates, pots, pans, or appliances. The lack of counter space is probably the complaint regular home cooks feel most strongly.
Even so, the basics are usually planned for. Most homes have a designated place for a refrigerator, and ordinary appliances will fit unless the household owns an unusually large number of them. Two people can often cook together as well, although they may need to coordinate their movements.
That does not mean Japanese people are satisfied with every small kitchen. Many would prefer a larger one if their home and budget allowed it. Spacious island kitchens and open layouts are widely admired, and they are often featured in model homes and housing advertisements. A large kitchen gives people room to spread out, store more equipment, and enjoy a greater sense of openness.
So the small Japanese kitchen is not the result of a cultural love of cramped spaces. It begins with the limited size of the home. From there, appliances became smaller and more capable, layouts became more efficient, and cooking habits developed around the space available.
The result is a practical response to a real constraint. A Japanese kitchen may look too small at first, but once you use it, you can understand why it often works better than expected.