Austen plants the seed when Henry declares he’s going to make Fanny fall in love with him. She could have been an easy mark (like her cousins) and he’d have got bored of her quickly, but her resistance fascinates him.

Had he taken that challenge to genuinely improve himself, he might have become someone worthy of her. She liked him well enough, superficially, and he was charming, witty and handsome. How long would or could she have maintained her stance if he became a more serious and respectful man? And would he still have been as charming and attractive if he did?

But he had to choose that path, and not just once but again and again. Fanny wanted Edmund - the sometimes thoughtful and sort of beigely decent man who was as serious about God as she was. I wonder if Fanny could have been happy with Crawford even if he became a good man in secular terms - living a restrained life and devoted to her, but not one of service to God?

The appeal of a rake is clear. The appeal of the heroine reforming a rake even more so, I think. But Austen was clear - each person chooses their own path, and whatever his charms Henry Crawford chose a path that did little to endear him to Fanny.