If a movie doesn't work as well as its predecessors, it's not because the filmmaker didn't give a fuck. People pull this shit with Spider-Man 3, too. "It was so bad, but Raimi clearly sabotaged it because he was upset with Sony, he just didn't care anymore and deliberately made it bad!" No, he worked his ass off; the movie just didn't work. I don't think TDKR is anywhere near SM3 in quantity or quality of flaws, but neither of their issues are a result of "the director stopped caring." You didn't like the decisions they made or the end result of those decisions; that's not because the directors didn't give a shit anymore. There are much lazier ways to make a movie than TDKR.
If anything, I think that movie's problem is the total opposite: not that Nolan had nothing left to say, but that he had too many ideas he wanted to cram into his last outing, and not all of it flowed together especially well.