Some where I read the following.
Left to right due to cultures which first wrote on clay or paper with a stylus or pen-like device. A right handed person would not smear previously written data.
Right to left due to cultures which first wrote with a hammer & chisel on stone. Hammer in dominant right hand
Vertical due to cultures (example Chinese) which first wrote with a paint brush
Right to left due to cultures which first wrote with a hammer & chisel on stone. Hammer in dominant right hand
Vertical due to cultures (example Chinese) which first wrote with a paint brush