I'll pile on.

Stems and bars are not great applications for carbon. Why not? Because carbon is great for tensile strength but relatively brittle in side loads. Stems and bars need to be strong against side loads, but don't require much tensile strength in the material (compared to, for example, a frame).

Aluminum is a great material for bars and stems. To make a carbon piece handle similar side loads requires a BEEFY piece of material -- generally as heavy or heavier than the equivalent aluminum piece. Plus, the carbon piece -- which may not perform as well -- costs a multiple of what the aluminum piece costs. (But it DOES have that pretty weave to it!)