Higher capital cost for carbon, but lower labor cost. In the long run, carbon is cheaper.
I have a steel bike that is 7.0kg. I have seen one that is 6.0kg. With a UCI weight limit of 6.8, weight is irrelevant.
And on a completely different note (and absolutely not directed to you or your post), I give this thread another 5 posts before it becomes a carbon sucks and steel is real thread.
Most likely my next bike will be a carbon fibre frame, with 33 steel ones in the shed, one Mod bike will not be too bad... And on that one I could care less about the UCI weight minimum, I'm going to go with whatever it ends up, my guess 12 lbs. about.