Before 2000, every bike had threaded stems. It meant adjusting stem height was relatively easy even though it was a pain to change bars and configure cables.

Threadless stems made the latter easier at a cost. The bike factory usually cuts the steerer too low to fit most riders so a bike shop cannot customize a steerer to size. A stem riser is a kludge to do what the bike factory messed up in cutting the steerer to a predetermined size.