I worked in thermoelectrics for quite a few years. We would love to have sold modules to GM. Where they DO work well is in the little beer cooler refrigerators. Quiet, no moving parts, and they do not see big temperature cycles.
The Russians, years ago did make a successful TE Generator. They had a kerosene lamp with a bunch of modules and heat dissipating fins on the lamp chimney. It generated "A", "B" and "C" voltages for old tube-type farm radios so the Worker Heroes never missed a Radio Moscow broadcast.
The thing was as ugly as a barrel of )*)'s and wieghed 25 pounds or more but it did work.
But when you put them in a vibrating environment like an auto engine, those semiconductor dice are as fragile as old cheddar cheese.
Boy, somebody in GM's SUV marketing department sure missed the boat!