If you are going to get into a car crash, does it matter whether your seat belt is buckled or not? Even if your car has seat belts, if they are not buckled and worn correctly you will still be screwed. It is in China's interest for the US change from unbuckled to buckled to take as long as possible, even if it cannot be delayed indefinitely. During that transition period, it is when the US will be more restrained and discouraged from taking large actions that can speed the car towards a wall (US-China military conflict). We want to delay that as long as possible so that by the time the US is properly buckled in, China's strategic and military strength is as close to completely unassailable as possible.