Maybe there's an actual canon reason but my take is this.
The Borg, being a hive mind intelligence of sorts, know where all the cables are going and ran and it's in their memory banks what goes to what. So, in order to make it easy to change or fix things, they just leave the cables hanging around willy nilly as they don't need any guidance one which cables do what or go where. This also confuses ship boarders who might be trying to tap into a specific cable on the ship.
Idk ... It's stupid but so are the borg.
