In their mind, it's fine to keep spending, so long as they are still standing at the end. But if they stop spending now, it would only send the signal that they lost confidence in the spend so far and that would instantly tank them in the eyes of everyone, thus fulfilling the prophecy of failure that they must know is looming over all of this.

So the only way any of them will stop is if one of them dies first. At that point, it may be possible to change the narrative towards it being smart to hedge your bets on this whole AI thing a bit.