One of Jane Austen's purposes in her comedies of manners is to highlight the manners revolving around the project of getting married--or not getting married. A large generalized description of the male point of view toward marriage specifies that males of the upper classes, about which Austen wrote, in the late 18th and early 19th centuries (when Austen wrote and was published) required wealth and social prestige in the woman they sought for marriage, this along with beauty and a good nature. An equally large generalization is that women sought men with wealth, a dependable source of continuing income and a social level above their own.
Wickham demonstrates the generalization regarding men in a negative extreme. His wasteful, irresponsible practices and personal character required him to marry a woman of substantial wealth because he had none of his own; he had only a long and ever growing list of businesses he owed money to.
Charlotte Lucas demonstrates the generalization regarding women in the extreme in a different manner. Charlotte has no fortune to attracted suitors; she lives in a small country community with no friends to take her to London for the social season where she might polish her manners and appearance and meet suitors; she has no beauty of note; and she doesn't have a romantic sensibility or personality. She recognizes that her only hope of not being a penniless dependent old woman is to marry anyone decent with a firmly established occupation and place in life who will ask her. This is precisely what she does in marrying Mr. Collins; Collins may not be clever or charming, but he is decent.