Why is it that there are so many burns from heat rocks? What is it about them specifically? Heat pads/tape etc. even when outside under the tanks also heats the floor so that the animal touches the heated (as vs ambient heat). The heat also comes from below instead of above, so that "no heat sensors on belly" thing doesn't explain it. Nor does heat trapped under the reptile as both heat rocks and pads are underneath. Substrate makes a difference but some people use newspaper for snakes and tile for dragons etc.

Is it just because people don't use a thermostat?

I want to build a heated shed for large lizards for winter sleeping out of plywood and heat mats/tape/cable underneath it. I see people build these with pig blankets for large tortoises. I just want to know what it is about hot rocks that causes burns so I do not "duplicate" that fault in my diy projects.