Why do light switch buttons have up/down direction when it’s really a toggle function?

If you do a quick image search on your favorite search engine on "light switch" you get a large number of images. Most of them have up and down direction, to represent state. Up for on in the US, and down for off. This varies among countries and as an example UK, Ireland, Australia and New Zealand have it the other way around.^[1]

More advanced light switches operate in pair such as in stairs, where the direction gets out of sync. Then the original meaning of up is lost altogether. A better way would be to have a toggle button instead. Cultural differences and stairway switches would be easier to operate, with a toggle button.

There is probably a good reason for the directional button, thus the question:

Why do light switch buttons have up/down direction when it's really a toggle function?

^[1] Light Switch - Up or Down