It's either because the non-ad-driven tvs cost more, resulting in too few sales to sustain (because no lifetime revenue from data sales) or the lifetime revenue from data sales is so profitable that companies take the risk on being undercut by a market entrant that will sell dumb tvs.

My guess is that the vast majority of people will trade data for a cheaper price point every time (my wife is certainly one of these people), so the market just can't support the volume of sales necessary to make the price point of dumb tvs competitive.