The rotary dialer was designed the way it was not from human input point of view but to mechanically generate the different number of pulses for each number, necessary for dialing. Phones thankfully moved on with the arrival of electronics which allowed a more human friendly interface.

But we still use keyboards with the same form factor that was dictated by mechanical typewriter constraints. I'm not talking about QWERTY but the whole device. Think about your unnatural posture when writing both hands on a keyboard. We could do a lot better but for some reason things like split keyboards haven't caught on. Path dependency is one tremendous force.