Q: Why is it cheaper to run new tires than recaps?
A: Is this a trick question? The real question should be why is it cheaper to run retreads than new tires?
To that question I would answer the following: A comparable retread costs about 1/3 as much as a new tire tire. With today's technology, the miles per 32nd are very, very similar for like tread designs (but, sometimes the tread depth of a retread is less than a similar new tire). If retreading is done on a quality casing (premium brand tire, that has been kept at an acceptable inflation pressure for the load it was carrying), there is no reason it can not perform at the same level as a new tire.
Equal performance for 1/3 the cost.