[Wavery]

It is normal for trailer tires to wear more on the curb side of the trailer.

Highways are sloped for water run-off. Trailers mostly tow in the right lane which would leave the right side tire down-hill, taking more weight and more drag (as the TV tries to tow the trailer "up-hill").

Trailers and other vehicles with 4-wheels will show ~less of this because they "Track" better on the slope. A single axle (2 wheel) trailer will constantly gravitate towards the low side.

As stated by the previous poster, rotate the tires.