Writing top-to-bottom has advantages for all writers whose eyes are above their hands. The bit of the writing surface that's blocked by your hand hasn't been written on yet.

Extending that, heads have a much easier time moving left and right than up and down, since the motion uses the pivot joints. So, that means rastering left to right, then top to bottom, is the best match to the average reading and writing human (since right handedness is the dominant genetic trait [1]).

[1] https://www.nature.com/articles/s41598-018-37423-8