If you run the palm of your hand over the tread area can you feel somewhat regularly spaced areas that seem to be lower (cupped) than areas adjacent?
If so then I would suspect a worn or defective shock absorber (damper) or an extremely unbalanced tire/wheel assembly. This does not address the somewhat uniform tread wear around the outside edge of the tire.
If you can, grab a level that is at least as long as the tire is tall and place it vertically against the tire aligned along an axis that travels through the centerline of the wheel hub.
Does the 'level' check indicate if the top of the tire is leaning out or in? If, to achieve a level (plumb) reading, you have to bring the bottom of the level out away from the trailer then that likely signifies that the axle or spindle is bent along the vertical axis for what ever reason. This would concentrate wear around the outer edge of the tire. A worn or loose bearing assembly would typically show wear aong the inner edge of the tire.
Another possibility is that the axle or spindle is bent along the horizontal axis and that could show as increased or abnormal tread wear at either the inner or outer tread area around the circumference however this type of wear will likely add another measure of wear to the tread that usually presents itself by exhibiting a feathering of the tread blocks.
Now that said; as other have mentioned, check your wheel bearings and have the rig aligned by a professional.
Sorry for the long read!