There is a reason. OLED panels are still quite bad for "staying" images (burn-in). And not only that, there has been many other issues, which makes them hard to make outside of standard 55" TV sizes. Not many manufacturing lines for them.

Lenovo Yoga Gen 2 used to have OLED screen, and it was causing huge repairs. On Gen 3 it was removed and they took a long break before introducing it on other products.