For a time it was a new market, full of potential growth. Then it got mature, every one who wanted one had one and given the nature of the device (low cost/low performance) it wouldn't need to be renewed for some time. Some manufacturers went upmarket (bigger and more powerful devices for more money) blurring the line with their entry level laptops. It wasn't a recognisable market segment any more. At some point, the market must have both shrunk too much and merged into other segments for anyone to care. Mobile devices ate their lunch too I guess.