Nah, it's as popular as ever, but after you get that much money as Kishimoto has, eventually there comes a point where you say "I don't want to be protracting this shit fest anymore, and want to do something else". If anything, he probably would've quit a long time ago, but whatever contracts he had with the publisher kept him going.
They made out like bandits, and will keep doing so for the next year or so as the anime draws to a close. But IN JUST A FEW WEEKS, I WILL BE FREE. FINALLY.