one of the incentives for refraining from a 51% attack is the exchange rate of bitcoin itself. such an attack being carried out and publicised would very likely

one of the incentives for refraining from a 51% attack is the exchange rate of bitcoin itself. such an attack being carried out and publicised would very likely deal a major blow to the currency exchange rate. as these pools make money from mining bitcoins (that is after all their very reason for existing) they would then lose out financially in a big way. in order to make up for these losses they'd have to doublespend a shitload of bitcoin in exchange for stable assets. and the greater the doublespend problem gets, the more confidence in btc is eroded, which then, once again, makes the price plummet. thus, from my amateur perspective, this seems highly unlikely atm.