Somehow, a while ago I became interested in small and unusual keyboards. Usually they came as PCB kits which required each key switch to be individually soldered, however, and it seemed tedious to me to have to solder
(number of keys) * 2 points on the PCB for the switches (not to mention diodes as well), especially if de-soldering was required later.
Some time after that, however, pre-soldered "hot-swappable" keyboard PCB kits, which come assembled in a form that allows switches to be directly plugged in without the need for any additional soldering, became more prevalent, and the kits for some of the keyboards I had previously been interested in were updated to contain such PCBs. Therefore, I recently bought a fairly well-known "40%" keyboard, the OLKB Planck, from Drop (Massdrop).