Why does the inside of a car feel warm even on a relatively cool day?

One day I decided to put my thermometer inside my dad's car. It is an Infiniti QX60. I'm not sure if car type matters when it comes to internal temperature whether it be a coupe, regular car, mid SUV, and an SUV. A bus inside is bigger so it does not get as hot as a car does. I put the thermometer in the car on a 67-degree day in the shade. 2 hours later when I returned to the vehicle the temperature inside the car was 82 degrees. 82 degrees is warm and you have the option of opening the window to get the refreshing 67-degree air or turn on the air conditioning. If the temperature in my bedroom gets to 82, I turn the air conditioner on until it gets the room down to at least 76 degrees before I open the windows. Also, the windows were completely closed for the 2-hour test in a car. Before leaving the car, my dad and I drove for 30 minutes with all 4 windows open so the car did heat up by 15 degrees in a span of 2 hours even in the shade. What exactly causes this warmup? By the way, it was an early June day in New York City, and the same day we had a low temperature of 55 degrees. Now at 55 degrees, the inside of a car is about 75 degrees which feels pleasant.