Then you're not testing them properly. They are "doing" exactly what they were designed to do. If you were to measure the effects from a sudden bump, fall into a pothole or off of an unexpected curb, you might find that your decceleration will create several g's of downward force on those springs. At your weight, this might be 400 or so lbs, which would undoubtedly deflect the springs. Their purpose is to absorb those forces at a spring constant that reflects that intent. Your static weight is not the issue.

BTW, you wouldn't want the springs to deflect at roughly your weight, you'd wind up "bobbing" as you mashed the pedals under load. Ever followed a dual suspension mountain bike rider up a smoothly paved hill, expecially one with a low spring constant or underdamping on the rear shock? That bob is energy loss.

The springs on the Brooks B72 are stiff, too.