The tips of fighter aircraft wings travel faster than the speed of sound, deal with far more stress (from turns, explosions, etc.), and the wings I expect are more complex and difficult to manufacture - but they fold.

I'm not saying you are wrong, but by themselves those factors aren't entirely convincing to me.

(Also, the wings need to fold and unfold repeatedly over their lifetime; the blades could just be, in theory, shipped in pieces and then assembled once).