Bike wheels often develop slight wobbles. If rim brakes were really close to the rim, they would rub. So rim brakes are set up with a fairly large gap between the rim and the brakes. When you apply the brakes, there is a fairly large distance for the brake to travel before it contacts the rim. Because rim brakes are designed for this large movement, less force is applied to the brakes.
I’m not sure what this means, but I’m pretty sure it’s wrong.