If only one tire is showing bad wear, then a bent axle from curbing or a pothole etc. likely is the culprit.
Since both tires on this axle is showing bad wear, then it is like losing it's camber due to overloading. I would visit the scales as a first step to see. If it is only slightly over loaded, then the fix may be as simple as lightening the load, and hopefully the camber springs back. Or the camber loss could be permanent. Then you would need to get it recambered, or better yet replaced with a heavier axle to keep it from happening again.