for a couple reasons. FOr one thing, I see Bruce Wayne as Nietzsche's "Ubermensch", the superman, the ultimate human being. His superpower isn't money (Fuck SNyder) but his will, and his discipline over himself. HE is the anti-Hamlet - and while Hamlet is unable to act until it's too late, Bruce Wayne acts without hesitation, considering everything, but never doubting. So many people these days are helpless, cynical, nihilistic people who things there's no point in doing anything - Bruce Wayne is the opposite. Luckily, he has the immense wealth and power to actually do something.
However, does he accomplish anything? That is the question. If we take his opposite, the random, anarchist Joker, whom he is locked in eternal combat with, and pit them against each other, their two concepts will battle until the end of time.
A lot of people think Batman isn't the interesting character, but his villains are, or Bruce Wayne isn't interesting - but to me, Wayne is the ULTIMATE character, perhaps one of the most complex in modern mythology. He's just often not written very well. Same deal with Superman, but Batman is a little easier to write.
Like Nietzsche said, it's all about will, and Wayne has the ultimate will. He makes the world around him - not just because of his wealth, but in his worldview, and in taking action where so few of us do.