Isn't the blue pixels in the OLED the same as in a regular blue LED or
No. OLED are made by thin, usually amorphous, organic layers on a (glass) substrate,
the "regular" LED is an inorganic monocrystal (so a single regular structure), grown as epitaxy layer on either a silicon or saphire monocrystal substrate.
The monocrystal has way greater efficiency and long time stability (the Organic wears out rather fast compare to the monocrystal),
The OLED are way cheaper for a given area plus it is a matter of simple litography to form many different patches onto one common substrate (e.g. RGB matrix,...), so really usable for directly forming e.g. the screen panels. The OLED can easily be made as a stack of multiple individual LEDs (layers on top of each other), mainly used to boost the light output for the very low current density it allows, but also usable to combine different colors into one pixel, so making it of virtually any color desired (e.g. the bluish-green-gray for the small monochromatic displays,...)