Having just done a google image search for "nappies and plastic pants". Give it a try, most of the results are for adults and not children's products. Could it be that most people use disposable nappies/diapers for children these days. Could it be that the plastic pant market is predominately the adult fetish market.
Being older I still like to use terry nappies and plastic pants, a throw back to my bed-wetting youth, but these days I tend to use disposable myself for convenience.