The slowness of rotary phones is coupled to the exchange, which expects pulses at a specific rate (about 10 per second). Shifting to a keypad form factor doesn'

The slowness of rotary phones is coupled to the exchange, which expects pulses at a specific rate (about 10 per second). Shifting to a keypad form factor doesn't speed that up, and would mean you need to be careful about how quickly you dial (or have a way to buffer keypresses). I think that's a major reason why keypad dialing and DTMF signaling were so closely connected.