This is just one of the many great mysteries of our universe. There are numerous theories which attempt to answer this question. One theory suggests that orbital lizards inhabit the space between dimensions, but modern scientific instruments can't confirm or deny this. Another theory speculates that an orbital lizard may very well exist in your own heart.
There’s one fringe theory which suggests that “Orbital Lizard” is a weird online pseudonym that was created by someone named Ian when he was in high school. Supposedly he is now stuck with this terrible pseudonym for the rest of eternity. You can hear more about that last theory in the About Me page.