>>115369471It was a combination of factors.
If Justice League/Unlimited directly fits with BB's timeline and not a quantum reality, Bruce blames himself for not being there to watch Tim. Instead, Bruce was hanging out with the League and that caused him to spurn away from it after the whole Joker/Tim clusterfuck.
He drove away Dick irrevocably after fucking Barbara. Barbara eventually got tired of Bruce's controlling single-mindedness and Tim went on his own when he was old enough. The only person that put up with Bruce's shit was Alfred and by the time Bruce was in his 50's/early 60's when holding that gun, Pennyworth was already dead. Even Jim Gordon wasn't around. Bruce was truly alone.
When Bruce nearly put himself and Bunny Vreeland in danger by not being up-to-par with heart problems, that was the final straw. Being forced to use a gun; something Bruce loathes was just the tipping point of what he was denying to himself; he was simply too old to be Batman. He realized that he was nothing more than an aging man who had nothing to show for his efforts except an isolated mansion and nobody to be with.
If you even look at what Gotham looks like when Terry's a teen, street crime has somewhat cleaned up compared to Bruce's days. Even with the Jokerz, Gotham became a thriving metropolis of inner city life and industry again. The main problem was that crime evolved into more organized and corporate levels like Derek Powers and all those other figures pulling the strings.
