Limited market. Can't sell them to folks who want to read novels. Can't sell them to folks who want the full features of a tablet. Can't sell them to folks who

Limited market. Can't sell them to folks who want to read novels. Can't sell them to folks who want the full features of a tablet. Can't sell them to folks who want colour, such as comic readers. They are really only useful for reference books, and mostly of interest in academia.