Why does a book about AI begin with economic growth?

I don't think it's really possible to make strong predictions about the impact of AI by looking at the history of economic growth.

This introduction sets the reader's mind onto subjects of very large scope: the largest events over the entirety of human history. It reminds the reader that very large changes have already happened in history, so it would be a mistake to be very confident that there will never again be a very large change. And, frankly, it underlines the seriousness of the book by talking about what is uncontroversially a Serious Topic, so that they are less likely to think of machines taking over the world as a frivolous idea when it is raised.