Why does Charlotte Lucas marry Mr. Collins?

Charlotte marries for a comfortable establishment, not for illusion. She is clear-eyed about Collins’s folly and about her own limited options as a woman without fortune. Austen neither romanticizes nor condemns her: the Hunsford chapters show Charlotte managing a foolish husband with practical intelligence — arranging her house so his absurdities are tolerable.

Charlotte’s choice is the novel’s foil to Elizabeth’s. Both women understand the marriage market; they differ on what they will trade. Putting their decisions beside each other (and beside the entail subplot) keeps “Love and Marriage” from being only the Darcy plot. It is also why Charlotte belongs in the character guide as more than a sidekick: she articulates a theory of happiness Elizabeth rejects but cannot dismiss as mere stupidity.