One very well know top shelf carbon wheel company had one person and one person only who built up all team wheels.  They had many wheel builders but only one was authorized to build for the team. 

Carbon rims are a totally different animal than aluminum rims.  Alloy rims are extruded and carbon rims are bladder molded.  This, and the fact that carbon rims are so stiff you can't bend them, presents a number of challenges.

First, some background on wheel building.  After the rim is laced, the first goal is to get the wheel round.  The main reason for this is that the roundness largely determines the equalness of the spoke tension because the spokes radiate from the hub.  Equal tension is important because it's unequal tension that causes some spokes to get stressed more than others and the more stress the sooner they fail.  Normally this is done with a drill that is a screw driver bit with a center shaft.  That shaft, when used to screw on the nipples, pops the nipple off.  You go around the wheel and BAM all the spokes are equally threaded.

On a carbon wheel, the internal bladded often means the spoke holes are not of equal depth so the screw drive bit doesn't work that well.  Further, they are difficult to use because the nipple is inside a deep cavity and you can't see in there.

The second issue is, unlike an alloy rim, you can't bend a carbon rim.  You center the hub and live with the rim.  Although you still use the same tools and the process is very similar it's really a different process. 

The good news is that over the last 10 years since I started building with carbon, I've noticed that there are far fewer spoke issues even though I was building wheels to much lower tensions.  I am not an engineer but it would seem very likely to me it's a result of the stiffness of the rims.  On an alloy wheel, you actually ride suspended by the few spokes at the top of the wheel - which change as the wheel rotates.  Because the carbon rim is so much stiffer, it's my guess that more spokes take up the suspension process.

Also, because carbon is more fragile than aluminum (it is stronger but tends to crack easier) the spoke holes are much deeper.  An alloy rim typically has about 2 mm of wall thickness where the spoke hole is.  A carbon rim typically is 4 mm.  That extra wall thickness helps prevents spoke nipples from loosening.