How can we explain the awareness of some characters to actually change?
Jane Austen is nearly scientific in pairing characters and (contrastingly) mirroring them according to their level of what we, as readers, could dub "maturity".
Wentworth changes because he is mature enough to understand where his happiness actually could come from. Anne, in a way, changes because she has differentiated the counseling from Lady Russell form her own mature opinion. Yet, Sir Walter does not change, and neither do those who hold a high esteem of it. Why? Because, socially speaking, these women had a better chance to be accepted in a quite superficial society by sticking to their own ways than through changing and becoming better persons.
Hence, the answer is that society holds the last card in Jane Austen's world. It was all quite put together from top to bottom, and there was no questioning involved. Hence, whatever happened, went on.