At the time, I guess Josh Hartnett could have been a big enough name to take on a role like Batman.
Hartnett reveals in the past that he had conversations with the studios to play both Spider-Man and Batman, but he was getting tired of the pressures of tentpole movies and fame at the time.
More recently, he had a role in Showtime’s wonderfully gothic Penny Dreadful series, but back when Batman Begins was coming together around 2005, he was building a career out of prominent movies like Black Hawk Down and Pearl Harbor.