Question

Why Japanese use chopsticks and don't use spoons?

Answer 1

Because Japanese prefer to eat noodles and all these

Answer 2

For whatever reason, Chinese, Korean, and Japanese food preparation called for food to be cut into bite-sided portions in the kitchen rather than by the diner at the table. This makes chopsticks perfectly suitable. With no good reason to change the tradition, it's continued to the present. If nothing else, I guess it would reduce the expense of buying knives. You only need one or two in the kitchen, not one for every diner.