They go to more exciting and fun disciplines. Dressage is not attractive to most kids, the way jumping and even western contesting disciplines are.
And you probably never will, for the reason I noted above. Dressage will never attract kids the way other, more fun, more exciting disciplines do. That is not USDF’s or USEF’s fault. It’s no one’s fault, it just is a fact of life.
Hunters, jumpers, barrels, contesting, you know, the fun stuff. Dressage is too cerebral for most kids. Hell, it’s too cerebral for most younger adults.