Because not everyone has some ethanol laying around, but most people have a can of Off. There is nothing else in it other than deet, (which will do nothing to the finish), water, and propellents.
OFF works miracles for cleaning dry erase residue from an old stained dry erase board. Of course then you have to find a detergent cleaner to get rid of the grease left behind.
For sharpie on many surfaces, I've found that rubbing paraffin (candle wax) on the pen marks, then wiping off with isopropyl alcohol works exceptionally well. I have no idea why or where I learned it. Perhaps somebody who didn't regularly fall asleep during high-school chemistry could speculate as to why it works so well?

