I wonder if having a bearing that presses down from above on the work positioned directly in line with the centerline of the bit and rub-bearing and at 90 degreees to that line so it assists in keeping the direction of travel perpedicular to the diretion of travel.

It also keeps one's fingers away from the bit. Having cleaned up a couple of folk's 'leftover hand-burger' off of router tables in my past life as a woodowrking engineer, I like gurads on bits.
: - )