Here's why:
* The other children have been expelled: All the other children, due to their greed and bad behavior, have been eliminated from the tour. This signifies the failure of their materialistic desires and the danger of being consumed by greed.
* Charlie's kindness is revealed: Charlie, in contrast to the other children, has remained humble and respectful throughout the tour. This is directly contrasted with the downfall of the other children, showing his virtue.
* Charlie's connection with Willy Wonka is established: Left alone with Willy Wonka, Charlie is given a chance to demonstrate his genuine character. It's at this point that Willy Wonka starts to see Charlie's true worth, foreshadowing the eventual reward.
This climax builds up to the ultimate reward of Charlie inheriting the chocolate factory. It emphasizes the importance of kindness, humility, and genuine character, and the negative consequences of greed and selfishness.