Why don't you quote the whole thing before that part;
“After The Dark Knight, it was a much quicker phone call from the studio asking, ‘What about the third?’ ” jokes Thomas. “Chris really had to think about whether or not he wanted to do that; we were very happy with the way we had tied up The Dark Knight.”
Before launching into another Bat-installment, though, Nolan first tackled 2010’s Inception. Then he also took the time to look back to characters and plot threads he’d established with Batman Begins.
The decision was obviously made two years after TDK was done since he didn't come up with that decision until after he'd made Inception, and they well knew by then that using the Joker again was not an option.