It's probably because 80% of his drumming career has been with one band. Just not as much exposure as some guys like Porcaro, Weckl, Garibaldi and Gadd. In my opinion, Carter is just as good, if not better in some respects, but he's fully dedicated to DMB. He's one of my main influences.
Want a challenge? try covering "Dreaming Tree" or some other song with an odd time signature and his unpredictable, yet perfectly fitting syncopation. I've been trying to learn Dreaming Tree for some years now. It's almost like one improvised groove that never repeats itself. It's beautiful.