Brecht and Copyright

From David Mamet's book, The Secret Knowledge, which I was just previewing on his website:

As a youth I enjoyed—indeed, like most of my contemporaries, revered—the agitprop plays of Brecht, and his indictments of Capitalism. It later occurred to me that his plays were copyrighted, and that he, like I, was living through the operations of that same free market. His protestations were not borne out by his actions, neither could they be. Why, then, did he profess Communism? Because it sold.

This is funny and apt, but there's an underlying question, of course.

Why did the road to hell
sell so well?