Supply chain issues with OLED and RGB LED displays?

It seems the Alienware 13 with OLED display is currently not in stock, nor is the Precision 17-inch with 4K PremierColor display.  These features are both marketed prominently on their product pages.  Similarly for HP, their flagship ZBook 17 G3 shipped initially without the 4K DreamColor, which was offered a few months later ...

Just wondering, with these high-end displays, what is the supply chain difficulty?

Could it be a case of Apply blocking other vendors' supply chains, to cut off legitimate claim that other vendors offer the best-looking screens?  Or are these unique parts truly so difficult to manufacture to acceptable quality standards?

Maybe the problem is demand much higher or lower than anticipated.  However, that would not explain the initial delay HP announced for rolling out the feature on their models.