These design engineers are working with weight. A class D amplifier circuit can achieve up to 90% efficiency, so that 10% has to go somewhere. To design a fan free amplifier, it has to have enough meat in the heat sink to dissipate the 10% or it will overheat(and kill) the semiconductor. Or one can run a fan across a smaller sink and all stays well. Personally, I'd rather have the bigger heat sink so if Mr. Fan goes on permanent vacation my amp doesn't start smoking. The payoff is weight.