When working through the Introduction to Polynomials worksheet, I noticed that the exceptionally large x values are never included on the graphs. I understand that the exceptionally high values are for discerning how the function behaves, but is it unnecessary to include the high values in a graph?

You have to understand that after moving to the right past the rightmost zero, or to the left past the leftmost zero, the graph will move away from the axis with a rapidly increasing slope.
The main purpose of considering x values of large magnitude is that they show how and why this happens.
As you observe we usually won't use a graph scale that takes us into the very large x values.