The radiators look like a highly stretched paper accordion. Is it just because of how they decomposed, or is there a deeper reason?
From the horse's (Vought) mouth, the angle created between each panel and its corresponding scissor beam (20°) is to "provide structural stiffness":
The deployment is achieved by rotating the first panel 80° relative to its initial stowed position and rotating the first scissors beam 80° in the opposite direction. The scissors mechanism rotates alternate panels in equal angles but opposite direction until an angle of approximately 160° exists between adjacent panels. The angle between each panel and its corresponding scissors beam at the pivot pin is approximately 20° when deployed. This 20° angle provide the structural stiffness for a minimum resonant frequency of 0.16 Hz.
— Oren, John A., and Harold R. Howell. "Space station heat rejection subsystem radiator assembly design and development." SAE transactions (1995): 1086-1095. p. 7.
The radiators are jointed because they were launched folded up into a flat stack.
This screenshot from the official NASA visualization tool DOUG shows one of the radiators partially retracted.
This picture of STS-113 delivering a truss section shows the radiators folded flat.
This prelaunch photo shows a better view of the folded radiator panels.
(last two images are NASA photos)
This is a scissor mechanism, as used in lifts and pantographs. A fundamental property of the scissor mechanism geometry is that it cannot "open completely" (90* rotation of members) due to joint conflicts. The radiator could be designed to pack flat, or to deploy flat. But not both.