Because he's a rich vigilante who could probably do better things with his money than spend millions on inventions intended to help him literally punch (and roundhouse kick) crime out of existence. He, like a lot of 'superheroes' tends to cause a lot of collateral damage. Gotham hasn't really gotten any better since he started (or you know, he would have been able to stop after saying 'Yep, no more crime here!'). Crime seems just as bad as it was. Sure, maybe he actually is stopping it from being even worse than it would be without him, but again, maybe he'd have more luck using that money to improve the state of the city further.
Wonders what our world would be like if comic book-like mutants/superbeings existed?