PUtting in big efforts/accelerations on the last part of the final climb is going to hurt a lot
That would be a good reason to do it there – first rule of racing, attack when you’re hurting as everybody else is too. The reason for attacking earlier is that you’re a lot more likely to be marked on the final climb, and even if they don’t mark you, it’s almost impossible to get the sort of gap he’s aiming for. It’s a big gamble, but one he kind of has to try – may be to his advantage that he’s been forced into this sort of move when previous years he’s been close enough to hope to make gaps just on the final climb.