If a horse needs a wedge it usually has some kind of a problem, and a steel insert isn't going to help. Also, if a horse needs a wedge shoe, it will usually benefit from having the toe rolled or rockered. A steel insert will make that difficult to do and prevent the toe from wearing with a nice roll. That also applies to a flat shoe. Dealing with a horse whose angle changes drastically through the shoeing period is a challenging proposition.
Many horses grow little, if any, heel.
At the time of shoeing, the hoof angle may be okay, but given the time span of four or five weeks, the angle will be very low at reshoeing time. The horse will be stressed during the last one, two or three weeks. You will find at the next shoeing the hoof hasn't lost as much angle and the difference in angles from the beginning of the shoeing period to the end of the shoeing period didn't change as much as the angles did before. That being the case, the horse will move more consistently throughout the shoeing period - very important for a show horse. 3 shows a foot fitted with a wedge shoe and the toe is rolled with a slight rocker.