My theory is because you are the only person that never hears your voice as others do. We grow up listening to our own voice conducted through the bones of our skulls, not primarily via the atmosphere as others do. Remember the first time you heard your spoken voice played back? Most people are not even convinced it is their voice!
Because of the original enginner settings in your brain, the ears trick you. You think you sound one way, because you actually are hearing 2 monitors of your voice, from vibes inside your head and the actual sound from your mouth. Which actually puts a short delay onto your voice making you think it’s fatter than it is. The internal mixer in your brain mixes this down to a pleasing sound with tons of effects and enhancements, including the ol’ pitch shifter for note correction. Then when recorded on external equipment such as n-Track and your 'puter and reality sinks in, you hear yourself as others do, you cringe in horror saying what the f&#k happened? That can’t be me! I sound better than that don’t I?
This is an exerpt from the book, 'YazMan, a clinical study of a man with no brain"