Why does Elizabeth now consider that Mr Darcy would have been an excellent choice of husband for her (Chapter 50)?

In Chapter 50, Elizabeth believes that a relationship between her and Darcy has become impossible. As a result, she can think more clearly on how perfectly suited she and Mr. Darcy would have been for reach other. "His understanding and temper, though unlike her own, would have answered all her wishes. It was a union that must have been to the advantage of both-by her ease and liveliness, his mind might have been softened, his manners improved; and from his judgment, information, and knowledge of the world, she must have received benefit of greater importance." She compares this vision of "connubial felicity" that she would never have, to the misery that her sister and Wickham would certainly have, and feels nothing but sadness for her own plight and shame of her family.