As I understand it, energy that creates a temporary cavity is often ineffective, because elasticity of tissue may often allow tissue to stretch beyond the temporary cavity without taking major damage.
Most handgun rounds do not have the energy to exceed such limits (unlike most rifle rounds, which can really tear things up). So, energy that does not directly contribute to creating a permanent wound channel may merely be expended without lasting effect.
Also, while energy is required for work, penetration is affected more by momentum, sectional density, and bullet type.
Last, those handgun rounds which can reach levels of energy that can really do extra damage, typically are hard for the average shooter to control - and the average shooter may not be willing to practice enough to get a good hit with the first shot.
Even good shooters will have a harder time with follow up shots with heavy magnum type loads.