We have carbon drive shaft, yno carbon axles?
 

Is there a reason why it can't be done?

Lighter and stronger axles seems like a two way bet to me. Your going to attract the power crowd and the less weight crowd.

Because the axles are exposed to stone impact damage while the prop shaft is safely tucked up out of the way.

Carbon fibre is very sensitive to sharp point impact damage.

Also, the axle shafts are so short the weight saving wouldn't be worth the expense.

Driveshaft shop makes em, just sayin' CF?.no for all reasons listed above but still built to 600hp+