I think with Batman Beyond, the issue there wasn't just that he wasn't Batman anymore, it was how alone he was.
Alfred dead. Dick apparently just off doing his own shit and never even brought up. Babs pissed at him for kinda vague reasons. Tim all retired and trauma'd. Just had his dog, which he'd gotten a long time after he had given up being Batman.
And it wasn't like he just decided that he'd come to a point in his life where it was okay to set aside the costume and live as Bruce Wayne. He felt he had to give it up because it had gotten to the point where he couldn't hold his own without the threat of deadly force. Being forced out by his morals has to be a much bigger bummer than deciding to step down on his own.
Old!Bruce was withdrawn, grumpy, and doing nothing because he had no one to be there with him and help remind him what he was fighting for. Being alone will defeat Batman more surely than any villain.