Power
CPAs have the power to destroy. All you have to do is print "fail" on an audit, and a CEO's career is more or less over. The prospect of potentially bringing down a fraudulent CEO might be motivation enough to consider this career path.
There are other ways you can become powerful as well—if you have a unique understanding of an area that becomes a hotly contested political issue, you can become a celeb in your realm. Today, tax rates for hedge funds and private equity funds are "under investigation" by the government and by Socialists. If you're an expert in how complex financial packages are taxed and managed, you can find yourself as a sought-after voice or opinion leader in a given area.
You can publish books, give rubber chicken dinner speeches, and be quoted in fine rags like the New York Times. Maybe your calendar overflows. You no longer have any open slots for the clients whom you used to bill $300 an hour. Maybe your rates now go to $400 or $500. Or more. If you're saving them tens of millions in taxes, almost any price is "cheap" for your services.
And then, what if you go for the MasterStroke Kill (chess term)? You hire everyone who is truly an expert in this arcane, complex, and lucrative area and your firm "owns" all of the brains in this arena. There is simply nowhere else for clients to go (at least for a while, until competitors find a way to compete)—maybe your firm can charge $1,000 an hour and force-bundle other services which clients have to buy if they want an hour of your brainiac time.
It can happen. It does, every so often. And careers are made from it. As Steven sings, "Dream on."