Just please take a good look at the colored chalk illustration commissioned by the publishers for the cover of this book. Better still, consult the helpful close-up below.
Given the context it's a fairly minor point that the woman depicted in the green business-suit has a left arm long enough to let her scratch her ankle without bending over. She NEEDS that big arm, since she is bearing half the burden of a piece of carved stone that looks like it weighs about the same as an automobile.
This green woman and her faceless compatriots on the far side of the stone, what are they about to do? Drop the stone into place, clearly. It is a metaphor, see? They are "building" (with their leadership) the "high-achievement" environments promised by the text.
Are we then to judge the worth of the text by the plausibility of the cover art? That Roman Arch is LEVITATING! Do you suppose the artist really believes that the keystone of the arch got dropped in at the end? Roman arches were supported (from underneath) by frameworks of wood until the stonework was complete. Then the wood was removed and – by a simple but marvelous balance of forces – the stones could support themselves up there in the air, which (as we all know) many of them in Europe are still doing 2000 years later.
All right, assume the graphics person is ignorant. And discouraged. Drawing covers for textbooks is probably pretty discouraging at the best of times. There still must have been a few dozen other people approving this design before it got sent out into the world. And they all apparently thought it looked just fine to have three smudgy stick figures supporting thousands of pounds with their bare hands while standing on a pair of projectiles that can only remain where they are in complete defiance of gravity.