He's been depressed his whole life. His dreams are filled with horrific images and the echoes of gunfire. Bruce Wayne basically became Batman because his parents were murdered; we've seen it countless times in comics, TV, and film already. Michael Keaton's Batman didn't like to discuss it; Christian Bale's Batman couldn't
stop thinking about it; Ben Affleck's Batman kept visiting the morgue. Zack Snyder opened Batman V Superman with a lengthy closeup on Martha Wayne's pearl necklace intertwined with her killer's gun. What's that you say? Oh, nevermind. Batman actually shot his parents in cold blood.