they either bought the (I think flawed) economic theory that this is needed
You’re putting me in the difficult situation of backing up the CCP on this one, but how could it not be needed? They kneecapped birthrates for a whole generation, and never recovered. Unless they fix birthrates or start allowing immigration, they have no other recourse than forcing people to work longer. Either that or they actually start acting communist and redistribute wealth so that the soon-to-be retiree generations can weather the storm.