It seems that The Structures of Letters and Symbols throughout Human History Are Selected to Match Those Found in Objects in Natural Scenes. This is a large-scale example of ecology shaping communications technology.
This sort of effect also occurs at a much smaller scale. Compare the geometric patterns in the paintings in the Morgan Picture Bible of Louis IX to those in the Marc Chagall Bible Series. The artists that produced the Morgan Bible primarily illuminated books. Marc Chagall primarily produced individual paintings. Not surprisingly, the Morgan Bible’s paintings look a lot like text, while Chagall’s don’t.