Why is the inside bottom of the cutlery stand recessed into a concave shape?

The outside is a straight-falling cylinder, but the inside bottom surface is gently concave^[1]. This craftsmanship was designed so that cutlery does not slip and rotate inside the container^[2]. When utensils are put into a container with a flat bottom, the tools naturally tend to easily spin around or slip sideways due to the weight of their handles. By concavely lowering the center of the bottom, the tips of the utensils gather toward the center, holding them upright without the handles scattering in all directions.

The stand comes in two types^[3]. The slanted type, with a diameter of 6cm and a height of 11.5cm, has an opening that is slanted low, making it convenient to grasp the handles and take out even shorter utensils^[4][5]. The basic type, with a diameter of 8cm and a height of 14cm, has ample depth, making it suitable for holding long chopsticks or cooking utensils^[6][7]. The thickness of both is 1.5mm^[8][9]. Weighing 230g for the slanted type and 430g for the basic type, they are heavy enough that the container will not tilt to one side or tip over even when long utensils are placed inside^[10].