umm, could be where you're riding: is it east coast or midwest ice? That stuff's really abrasive.
Could be the type of wax you used may be wrong for your area/conditions.
Could be you just didn't do a very good job...did you hot wax with an iron?
Finally, some base materials are better than others...what brand board is it and are you sure it's a sintered base and not extruded?