And the reason they didn't was that they evolved from typewriters that relied on a forward/backward spin to move up and down (except for the carriage return lever). We're lucky that the original terminals didn't have a scroll knob on the left and right of the machine to move up and down and a lever to move to the next line or we would have been stuck with that concept for years and the laptop may not have been invented because the knobs and lever would have required some elevation, which means the whole thing would have had to have been bigger.
I used a scroll knob to move up and down (and left and right) on my Blackberry in 2000, and it was awesome. It's dramatically better than using arrow keys. It's a real shame the original CRT terminals didn't have scroll knobs. It would have dramatically improved the usability of computers throughout the 1970s and 80s.