Poland would love to be in the fight, but they know they would drag everybody else in, so they have to sit back and take it.
I’d not be sure that if they enter the fight anyone would follow... promises nonetheless.
Remember 1939.
And the rationale would be stronger this time: if Poland enters the war and is joined by NATO, the war will be nuclear.
On the other hand, if Poland enters the war just by itself... well... remember 1939 again.