Why did monsieur loisel expect his wife to be pleased to receive the invitation from the minister of education?

Answer 1

Because he knows that his wife is unhappy with what she has got, knows that she aspires to be a woman of a higher class and thinks that getting her the invitation to the ball with satiate that. It is also possible to say that he loves her very much, and that is why he worked his hardest to get her the invitation, even though they weren't really invited.

Answer 2

M. Loisel anticipates that Mathilde, his wife, would be overjoyed by the lavish party invitation he was able to arrange at the ministerial house. He is aware that his wife is dissatisfied with her basic, working-class existence. He is aware of her aspirations for comfort, riches, and socializing with the affluent. He therefore believed she would be overjoyed by the invitation.