Update: just after posting my article, Samsung annonced the Gear Fit, a fitness band with a 1.84" Super AMOLED panel. Perhaps my reasoning was all wrong, and high-resolution, color displays may take over this new market as well.
Passive Matrix OLEDs (PMOLEDs) use a simple driver, which restricts the resolution and efficiency of the display, but also enables it to be produced easily and relatively on the cheap. The first OLED displays on the market (in 1998) were PMOLED, made by Pioneer, used in car audio systems.
The PMOLED market grew in the past, up until 2006. Back then, the main application for those displays was the sub-display on clamshell phones. But then Apple launched the iPhone, and since then the clamshell design lost its popularity very quickly - and the PMOLED market is in decline ever since.