Why is tofu important to japan?

I'm a Japanese,so I will try to answer the question.

Tofu is the one of the key foodstuff in Japanese cuisine. Used for popular cuisine and frequently.
For example, it is one of the most typical ingredient for the miso soup which is the most popular soup in Japanese cuisine. Hiyayakko is the cuisine which is just tofu with soy sauce and one of the most famous fixing. Yudoufu is the hotpot which is the cuisine with tofu and vegetables and one of the most famous hotpot in Japan.

There are tofu in every grocery stores or even in convenience stores in Japan.
When I first saw the tofu in American supermarket, I was surprised because they treated tofu as the substitution for the meat. For Japanese, tofu is valuable not as the substitution of something but as itself.