First, "kneeling" is a kind of etiquette in Japan.
In Japan, "kneeling" means "sitting in the front seat", which is the most formal sitting posture among all kinds of sitting postures and a kind of etiquette of the Japanese. Japanese official sitting posture, kneeling, hips on heels. Thumb and sole should overlap. Men's knees should be slightly apart, while women must be closed. Although this kind of "upright chair" has certain influence on the leg shape, it is good for the body. For example, the correct sitting posture will eliminate the fat in the chin and tighten the lower abdomen. The reason why Japan has such a custom is that in the past, Japanese people wore kimonos, and the hem of men's kimonos was relatively open, while women's kimonos could not be opened. Therefore, women can't lose their shape at any time. Take small steps every time you walk, and you can only sit on your knees when you walk, so as to keep the kimono beautiful.
Second, "kneeling posture" is influenced by China.
The trousers worn before the Northern and Southern Dynasties in China are called "shin clothes", which means legs, and shin clothes are clothes worn on legs. But the clothes on the calf are worn by one leg, so there is no crotch. Sure enough, Jing Yi had to wear a skirt-like "petticoat" outside, which mainly covered the crotch, which explained why the ancients knelt down. We all know that Japan has always been influenced by our national culture, and many of their cultural heritages have been learned from our country. Kneeling posture spread to Japan and is still in use today.
To sum up, the reason why Japan has always maintained this kneeling posture is because kneeling posture is a cultural symbol of Japan.