Doing a 51% attack is like shooting yourself in the face. You get absolutely nothing out of it. If you control enough hashing power to perform that, why destroy the very thing that's making you money?
By denying every other miner any profits you can almost double the bitcoin income. This will make other miners give up, and then you can gradually turn off some of the miners and save cost. The risk for this is already very high but it doesn't seem to influenced the price. It's hard to tell if this is because the majority is in denial about it or just doesn't care. If it's the latter it means it would be very profitable.