That's exactly it. Cable management is a top-down design philosophy. The Borg are a collective that organically integrates biological, mechanical, electronic, and any other systems that they find useful--it's quite literally the polar opposite of a top-down design philosophy.

It would be more surprising if the Borg had tidy cable management, because that implies some hierarchy. Actually, the Borg cubes are a little out of place in that regard. Spheres or fractal-ish structures would make more sense.