They had modal menus back then, they just didn't display them. You had to memorize which obscure symbols to press, to change various settings. For example, in the 1970's, HP's calculator watch required pressing ⯅• to switch between 12 hr and 24 hr modes, or A⯅A to clear an alarm.

In the 80's and 90's, when sixteen-segment and dot-matrix displays made displaying text easier, calculators started displaying menu items, so you didn't have to memorize the sequence.

Since then, we've moved on to full-color high-resolution displays that can handle any text of any language, and the menus have more-or-less switched back to memorizing a sequence of which obscure symbols to press, I guess because some people think they look cool? Sometimes there's no menu at all, and you just have to memorize finger movements.