Inside area of a cross-section of the barrel of my floor pump = about one inch.

Pressure I inflate my tires to = 115 PSI.

Do the math. It's not my entire body weight, but it might be yours! It's awkward, more than it really takes strength, with a floor pump. (Think of parallel bars, or a narrow staircase, and you'll realize that you can easily support your body weight with both hands. But with a pump, you have to bend over, have your hands close together and pronated, etc.)

+1 to what Andrea said ... all of it.