Why are there round-headed kitchen knives?

This depends on making the choice more convenient for more people. Some people prefer this kind of source kitchen knives. Only when there is a consumer market will businesses produce them.

Because there are many people who like this source of kitchen knives to pick up food. As long as there is a market for consumption, merchants will produce it. As long as they can make money, capitalism will obtain this means of production. After obtaining the means of production, it will produce it.