There certainly is some money in juggling. The article mentioned 50k starting salary at cirque du soleil. But maybe working in concrete lets him spend more time with his family for roughly the same amount of money (or more).
In my youth, as a devastatingly mediocre musician, I got the opportunity to spend some time with a band. The sex and drinking looked fun, but the nighttime hours, and never being able to settle down with a nice girl and start a family, blow.
This article is much more about the journey of his life and the journey of a journalist to answer the question. The final answer means very little; there are a myriad of reasons he quit. Perhaps you should read the article. It's very enjoyable.
Good point. The previous title ("Why did the greatest juggler alive quit to open a concrete business?) wasn't much of a question, so we changed it.