What makes the new car hotter inside for drivers?

May be...

“I saw Brian, and even Junior needed a second to breathe. It’s just tough,” Hamlin said. “We’re trying as drivers to stay hydrated, but these cars are just way too hot.”

Glad to see you back Beth, you have been missed dearly!

Can we get NASCAR to do a recall like the regular car makers are forced to do?

The old car rules allowed the teams to evacuate the pressure under the car causing a lower pressure and more downforce. This resulted in engine, radiator and exhaust tubing heat being removed along with the air.

The new car has higher pressure under it resulting in less air movement so more of the heat generated can be absorbed by the floor of the car.

To a lesser degree the "yaw" put into the cars shifts more heat away from the right side over to the left side of the car.

The new seats have also greatly decreased the air circulation around the drivers.

Drivers are going to have to be in shape and hydrated to be successful this summer.

my guess is that the protective foam insulation now built into the sides of the new car keeps more of the heat generated from the engine inside the cockpit, like a thermos, and that wasn't as big a factor in the old cars. that combined with a design that allows even less air to circulate in the cockpit through the windows than ever before (to cut down on aerodynamic drag), probably makes them quite a bit hotter. but that's just my guess.

Foam in the doors.... and the drivers seat is closer to the center of the car