It's not an effective technology ...that's why
It is an effective technology but its limited to defending coastal targets at best 300-500 km assuming you can track object in real time within that radius ...its good for the chinese to deter USBG being station close to its coast during crisis.
Let's take for example the Chinese "carrier killer" missile DF 21D :
Firstly, (unless it is using a nuclear warhead) it is going to need terminal guidance in order to fine tune the warhead’s trajectory when it reenters the Earth’s atmosphere. This is true regardless of how well China needs the position of the target carrier - the target it wants to shoot at.
AShBM does not re-enters atmosphere but boost glide at 40 Km and tries to be at a place where its Homing Radar Active seeker can track the Ships , ofcourse it has to be give a good intelligence on the probable location of ship so that it can be there at shortest possible time and then rely on its homing Radar to track ship and dive on to it.