I've wondered the same for a while, but the best I can figure is that up to this point the use of super capacitors hasn't been worth the added complexity. Also

I've wondered the same for a while, but the best I can figure is that up to this point the use of super capacitors hasn't been worth the added complexity. Also, the power output of Li-ion batteries has gotten so high that the supercapacitors only offer power benefits for marginal use cases.