It is a design decision. You hold the Hu-card up and read from the title, to the art, to the little writtings, and then continue reading. In East Asian cultures, they read from up to down.
They probrably noticed how people, was flipting the card, the wrong way. Like a VHS cassetter, or how a western reads. In Japan, and other places in the East, like Hong Kong, books and writtings for a while was printed the same way westerners printed, and wrote books. They saw people handle the cards, and realized what they were usted to. Reading the cards like VHS box. Maybe some cards that was released during this time, or common shaped items could also read this way.
The same reason for the original MarkIII plugs from right to left, once again linked to the east asian writing. However once again, they decided to go western, instead of sticking with their eastern values. The PCE, units all have one entry point because most people who brought the system was not going to be playing two players.
So all of three varibles point the, direction an East Asian person reads and write.
This could be applied to the sound phonics and tones as well.