The miners are incentivized not to undertake the attack you envisage because the outcome of such an attack is a fairly routine modification of the consensus pro

The miners are incentivized not to undertake the attack you envisage because the outcome of such an attack is a fairly routine modification of the consensus protocol to an alternate Proof-of-work algorithm, which instantly renders all of the attacking miners hardware obsolete. They quite rightly want to avoid any strategy that might lead to that outcome.