Almost all human being are right handed?

I think it has to do with brain structure.

The part of the brain that controls handwriting is in the left hemisphere of the brain in 90% of right-handed people. Like you said, the left brain controls the right side of the body, and most people are naturally right-handed. That makes sense. It's also in the left hemisphere for 70% of lefties, and I don't "get" that. But I hope the info's helpful.

Link is below.

I'm not sure, But in catholic schools at one time being left handed was considered the devils work. So people had to write with their right hand. Years later they still tended to use their left hand.

It mostly comes down to what hand the teacher used to teach you how to write. If your teacher was a lefty, the students are more adept to also become leftys.