Because there are no fours.

A boy cannot begin playing ball too early. I might almost say that while he is still creeping on all fours he should have a bouncing rubber ball.

… he trotted down the hallway on all fours and started in on his second favorite pastime, conversations with plumbing. Just what I needed: Stone, the Toilet Whisperer.

When a doting person gets down on all fours and plays with a puppy’s rubber mouse, for instance, it only confuses the young dog and gives him a sense of insecurity. He gets the impression that his world is unstable, and wonders whether he is expected to walk on his hind legs and learn to smoke cigars.

The final goal of physical education is to make strong beings. In the purely physical sense, the Natural Method promotes the qualities of organic resistance, muscularity and speed, towards being able to walk, run, jump, move on all fours, to climb, to keep balance, to throw, lift, defend yourself and to swim.

I know that I have had friends who would never have vexed or betrayed me, if they had walked on all fours.