Why do kindergarten and primary school teachers force left-handed people to write with their right hands?

There is no law requiring you to use your right hand.

But the typesetting method of modern China characters is really more suitable for right-handed writing: because if you write with your left hand, it may stain the handwriting that has just been written and has not been dried, and it is not easy for you to write a flat line (you can try it with your left hand). Writing from right to left in ancient times was suitable for left-handed calligraphy. There are also some small truths: for example, if two people have a table, one writes with his left hand and the other with his right hand, it may be easier to occupy space.