UV degrades the epoxy. It is the epoxy that stabilized the fiber matrix. if that breaks down, you have a near equal to a bundle of carbon threads. this is separate from the clear coat paint failing.
There is a magazine that has had articles about and surrounding this over the years, Professional Boatbuilder. There was a short time where guys who bought carbon fiber rigging wanted to show off the carbon, that is passe.
Also, online forums for the "rice burner" Asian Import hot rod car crowd lament the short life of carbon fiber hoods, outside mirrors, trunk lids where the weave is visible and the sun attacks.
True, a car will probably see much higher UV load over time than a bike, but the process is the same. Kestral and Calfee where they painted the frames - a terrific job of protecting from UV.