1) It is arguable that carbon fiber frames are plastic. They certainly are in the sense that fiberglass body panels are - thermoset resin over layers of chop or fiber. But they have to be hand fabbed, which is expensive and time consuming. The also have the limitation of being one-sided in that the finished exterior surface will be dimension but the interior won't.
2) Injection molded thermoplastics often have limited stiffness, and in order to achieve real stiffness, must be "filled" with some sort of fiber (often glass fibers) to achieve truly rigid parts. Plus you get a 2 sided part with intentional features on both sides.

I know Lemond has been in partnership with several entities on a next gen carbon fiber technology. If I were betting on what it is, I'd think they're close to commercializing an injection molding process for carbon fiber components, which would make a molded plastic bike both a reality, and just as light/strong as existing CF frames, with a potentially lower cost.