Here is an honest and simplified answer. I will attempt to leave the technical discussion out of the answer. Even if the air leaving your ducts is 59 degF, it is not 59 degF in your car. Research
kinetic energy a.k.a temperature, or just get a thermometer and see for yourself. There is no way the temp in your trunk is near 60 degF. Seeing as you live in a hot climate, you ...