John Burke sits in a chair all day because he?

From the text:

John Burke was what was known as queer-headed. Black and ageless, he sat rocking day in and day out in a mindless stupor, lulled by the monotonous squeak-squawk of the chair. A battered hat atop his shaggy head shaded him from the sun. Usually John Burke was totally unaware of everything outside his quiet dream world.