The reason for the falling switch and bottom sitting switch was because the fall was a momentary scoring switch while the bottom switch was part of a sequence complete series of switches (that can't share a row or column.)

It's a carry over way of doing things from the EM era. If a temporary scoring switch is held closed, it could either bounce, OR, the same score value switch was used in multiple places and if one stayed closed, it would blind the game of all the others.

Later, they used the bottom switch (as a leaf switch) as both through software.