They were reading. Just not reading written words.
They were reading animal signs, weather conditions, position of stars, behavior of the elements, daily and seasonal rhythms, human expressions and gestures, and man-made markers and symbols that evolved into writing eventually. Not to mention omens in the flights of birds, arrangements of clouds, sacrificial animals, and so on, and the effects of rituals meant to reveal messages from the gods.
There was plenty to attend to and interpret before the ABCs came along.