Hi Eric, What Gary says makes the most sense to me. From your description it does sound as if something is out of alignment. The friction is normally spread equally over the entire surface which results in equal wear straight across.
The amount of misalignment would not even have to be visible to the human eye. You didn't mention how long it took to get to this state but I'm willing to bet it didn't happen overnight and was over a long period of time.
Axels take a lot of pressure and if not high tensile metal they can end up getting slightly bent, but in your case you mention that the side wearing down isn't even your dominant hand side, which does in a small way exclude the axle from being bent from user pressure. Also check the wheel bearings on the wheel for more wear on one side than the other.