They took the whole printing idea and just made everything faster, sometimes by duplicating hardware (many more hammers), other times by increasing speed (paper feed).

Some of the "scaling up" is obvious: a lot more metal in a drum or band than a simple print head, but the difference in cost would be negligible next to how much they could charge rental (or even sale) for being able to make it print so much faster.

Far from the first time us humans have done this with technology. Modern gasoline engines can be insanely complicated, even before they got tiny computers everywhere. One of my favourite purely mechanical examples is Bosch's K-Jetronic fuel injection system, used by a wide range of performance engines in the 70s and 80s.

Another example I love is helical scan videotape. Four head drums needed four rotary transformers between the two halves of the drum. And later prosumer VCRs had way more than four heads...

Wade.