Why are energy pyramids shaped the way that they are?

They are shaped like triangle to show how the amount of useful energy enters each level

The energy pyramid is shaped like a triangle to show how not all the energy of one organism transfers to the next level. The triangle decreases in size going up as does the amount of energy transferred. A graphical model that is shaped like a pyramid to show how the energy flows through a food chain, how the amount of energy is decreasing and becoming less available for organisms as it enters each trophic level, and how much of the energy in the ecosystem is lost to the atmosphere as heat.