How can they generate less heat when the break function is to turn movement energy via friction into heat? Energy needs to go somewhere and vibration and usually noise are not enough to make much of a dent wrt. energy.
Problem with disc brakes is they have a much smaller contact surface and the heat in the area where the calliper pinches is very focussed. Shedding that heat is much more inefficient as the steel takes a while to conduct the energy to the rest of the rotor. This is why brake fade happens much quicker for those brakes, and why there is a lot of tech on fancier disc brakes for shedding that heat.
Another benefit of drum brakes is as they heat, they expand and push the drum tighter to the pad, effectively helping you brake harder as they start to fade.