King of the Hill DVD sets

Does anyone know why King of the Hill has only been released up to season 6 on DVD? They have 12 seasons’ worth of material so far and I’d like to have them all in my collection. Does anyone have any information on tentative release dates, or if they will be released at all?

The Simpsons is also being released on a slow schedule. They most recent season released on DVD was the 1998-1999 one.