Why haven't we seen carbon fiber butts proliferate the market? I'm talking about a CF tube with no paint on it, so it will look just like all the CF shafts. Would they be too light? I suppose they could be filled with something like the shafts are to get the weight right? Is there some other reason?

The closest I've seen is one of the Chinese brands I believe has an ugly painted CF tube with wood inside, and it was the old style CF with the cross hatching from the 1990's. I may be remembering wrong on this one.