Originally Posted by alcjphil

Spoke protectors are very thin and are contoured to follow the dish of the spokes. A disc rotor is much thicker and perfectly flat. Your derailleur would probably hit the rotor when you shift to your largest cog

Originally Posted by Chuck M

Amazon has more spoke protectors under 10 bucks than you can shake a stick at. If you want something blingier than plastic, chrome ones are about 5 bucks more. I don't know that it would be worth the effort for most people to try to use a disk brake rotor unless they want to aggravate the people the eschew spoke protectors AND disk brakes.