Let's give a little credit to Mrs. Bennett for knowing what her daughters needed and, although clumsily, going after it like a good mamma. Girls like hers had no secure future except under the care of a husband. None. Charlotte Lucas knew this and so did everyone else. I think AD inserted the conversation between Jane and Elizabeth in the bedroom at the beginning of the film (not in the book, every contemporary reader woould have been well aware of the situation) so that viewers of our time would get it. In a small community like Meryton there wasn't much choice so Mrs. B. did all in her power to latch on to what presented itself. In that way she was a much more concerned parent than Mr. B. who doesn't seem to have given much thought to the family future.