Because some men aren't looking for anything logical, like money.
They can't be bought, bullied, reasoned or negotiated with.
Some men just want to watch the world burn.
I must be honest that I was not a huge fan of Batman Begins, but to be fair I've only seen the movie once, so it might be worth giving it another try after liking the The Dark Knight so much. There is one final movie left in Christopher Nolan's Batman trilogy, and hopefully if will live up to the second in the series, and complete the trilogy in LOTR fashion. However, it's going to be difficult to top Heath Ledger as the Joker (he played the character better than Nicholson did, and that's saying something), but there are a slew of great Batman villains that have yet to get any play in the movie franchise.