because the original Macintosh didn't have arrow keys on the keyboard.

However, the very next keyboard they designed did have them: https://en.wikipedia.org/wiki/File:Apple_Macintosh_Plus_Exte...

I can't imagine editing text on a keyboard with no arrow keys to be any better than the horrible experience of doing it on a mobile device... which might be why Apple decided to add them quite early in the history of the Mac.

It's also ironic that despite justifying the menubar at the top of the screen as being easier to hit, they then totally missed the awkwardness of not being able to navigate with only one hand by using the arrow keys and the nearby return/enter. Watching someone experienced using Windows' file manager with only the keyboard is almost vi-like in its efficiency.