Clrnc
Partly because it's a trophy and so of course they want to win - the Invincibles always celebrated winning it in style too - but in Liverpool's case last year it's because they were facing up against the team they thought they'd be going head-to-head against (and for the Invincibles it was usually United they were beating at Wembley) and you don't want to give any sort of edge.
You can't just switch the intensity off and on at will. Facing City, 80,000 people, world watching, curtain raiser to the season - make sure you're on it!