Steerable axles on trailers weigh more, cost more and need more maintenance. The additional weight of 1500-2000 lbs takes away from payload. In Europe secondary roads are narrow and steerable axles are a must. In North America truck yards are expansive and even secondary roads do not have sharp curves so the cost benefit equation favors fixed axles.
One of the things stressed by good Class A driving instructors to their students is the importance of ensuring that the trailer wheels are moving at the same time as they pivot as the student backs up to avoid stressing those trailer wheels.
On steerable axles, the steer angle on the trailer wheels is remotely controlled and is programmed to mimic the angle of turn of the truck tandems though in the opposite direction. Hence backing such a trailer does not require any more skill than backing up a fixed axle trailer.