Very good question.
Courtship, while important to the novel, is not really the novel's central concern. Pride and Prejudice is a novel of manners, meaning it is a story that focuses on the social roles of a group of characters, how their words and conversations help define those characters' social roles, and ultimately, how well each of the characters succeeds at fulfilling their social roles.
- For the Bennet sisters, the social expectation is, of course, that they will marry well--but then again, they have to. Their father, described as an "indolent" man, has not saved any money for their upkeep, and to make matters worse, his estate is entailed, meaning that if he himself has no sons, the estate will not be inherited by any of his daughters, but by the next available male heir. In this case, that heir turns out to be a somewhat distant cousin, the objectionable, foolish, and insipid Mr. Collins. In this way, Mr. Bennet may be said to be something of a failure at his role: he cannot provide for his daughters, and is too indolent and indifferent to try to mend matters. Meanwhile, his wife Mrs Bennet--ignorant, foolish, embarrassing, and high-strung though she may be--is nevertheless rather a success, at least socially: she has married well, is secure at least for the lifetime of her husband, and surely one or the other of her daughters will marry well enough to take care of her and the rest of the girls, should Mr. Bennet predecease her. As far as Mrs. Bennet's social expectations are concerned, therefore, she has fulfilled them.
- The kind and intelligent Charlotte Lucas, who eventually marries the awful Mr. Collins (after Lizzy turns him down), on the other hand, is a smashing success: she has succeeded in marrying a stable man and achieving an establishment and financial security of her own--no matter how annoying the man she had to marry to get that security may be.
- Lydia is an abject failure at her role. She elopes with Wickham and thus tarnishes permanently not only her own reputation, but the reputation of all her family.
- Caroline Bingley, lovely, cultured, and rich, is also catty and rude to the extent that the brilliant match she hoped for, Mr. Darcy, is disgusted by her.
Courtship and marriage is such a concern for the Bennet sisters in particular because they are in an awkward place socially. Being the daughters of a gentleman, however penniless he might be, they cannot exactly go get jobs to better their situation; that would be absolutely unheard of. Their best hope is to succeed in the role available to them: that is, to make a good marriage, and achieve permanence and stability that way.
So while the courtships and marriages of many of the female characters are important to the plot of the story, Pride and Prejudice is less a novel about courtship, and more a novel about success and failure in one's prescribed social role, and the various faces that success or failure may wear.