This drawing went with a hypothetical. It was about putting a 1920 car under a glass bell where nothing could harm it for 20 years and what, dear young student, would that car be worth today?
Which gives you some insight into the mindset. Today this example goes the other way. That car would be worth a lot. The point the text was making, however, is that the car is outdated, outmoded and undesirable compared to everything else now on the road. An education, the book argues, isn't sealed and completed when you leave grade school or high school. One must keep at it, exposing one's self to the changing environment, to stay valuable and current.
This is an important shift to make, then as now.
Even still, a Model T snow globe might be pretty neat.