all the cold air still in the ducts is delivered to your living space and the cold metal ducts continue to cool the air as it is pushed through, even with the A/C system off when it reaches temp.
These past couple of days I've set the fan on continuous so it never turns off, and the A/C system cycles on and off much less than it used to. Now I'm not wasting that cold air in the ducts and just waiting for it to heat up before blowing again.