An ice maker is more complex than just manually freezing ice in a tray. You have a bunch of small motors and pumps and things that require more electricity to function, and all of that energy is on top of the energy it takes to cool the freezer (which a non ice maker refrigerator is already doing). Plus, all those things that are inside the freezer space are now generating or adding heat in the space youre using energy to cool, especially the water it’s continuously freezing to make ice whenever it isnt full.

A report from 2020 said that automatic ice maker refrigerators use 14-20% more energy than a normal refrigerator

It's the need for a thoroughfare through the insulation that makes it less efficient.