The problem is

if

a) The attack is unsuccessful, the attacker loses a lot of resources

b) The attack is successful, the value of Bitcoin plummets (perhaps people switch to an altcoin or hard fork Bitcoin with a PoW change), and the attacker still loses a lot of resources.

It's more worth it for them to just mine honestly and get honest rewards, unless their only goal is to harm Bitcoin, in which case people will just switch to a more robust PoW system (like multi algo, merge mining), so don't see what they will gain.