In college, I was taught that when we speak, because the sound is coming from inside us as well as being received by our eardrums, all our voices automatically sound lower and deeper to us in the moment of speaking than they sound without the accompanying from-inside vibrations.

A google search brought up this explanation.

When you speak, vibrations from your vocal cords resonate in your throat and mouth, and some get transmitted and conducted by the bones in your neck and head... Whenever you speak, your inner ear is stimulated both by internal vibrations in your bones and by the sound coming out of your mouth and traveling through the air and into the ears.

This combination of vibrations coming to the inner ear by two different paths... enhance deeper, lower-frequency vibrations and give your voice a fuller, bassier quality that’s lacking when you hear it on a recording.