[paulftw]

why couldn’t it be done on an off-the-shelf 28-byj-48 stepper?

The reason is probably explained somewhere in the article, I just can’t find where

[Joel_Mckay]

The 28-byj-48 were designed to oscillate air conditioner vents, and as such have an internal slip-clutch mechanism to add to the abysmal backlash of their gear box.

There is also the weight and energy consumption to consider.

People may be better off gluing a small bead to one side of a flip dot display. =)