...then why do the players try to get the crowd up and loud for important plays when a stop is needed?

I promise you that anything Bronco has to say about selling out the stadium is not about the money.

I think a full stadium adds to the home field advantage. How much? I don't know. And it might even be different for different players. But for whatever reason, the players and coaches think it matters. And they aren't thinking about the money.