A touring bike is stressed quite differently to a racing bike. The luggage system is held to the frame at the chainstay tubes. Ultralight steel tubing (Reynolds 753) is not used in touring bikes because it can't withstand the luggage loading. 753 was an excellent tube for TdF riders but not for tourists.
I'm sure you could build a carbon bike to take those stresses, it just wouldn't be an ultralight one.
The other problem with carbon fibre is mechanical damage to the frame due to drops and scrapes. I have had my steel tourer slide down a brick wall of its own accord and the paint was scratched.

Touring bikes are not replaced every year or 2, like elite racing bikes. Mine is 15 years old and many are older.

If you are considering light/day-touring bikes for non athletes, then certainly they can be build lighter than professional grade bikes and lighter than the UCI mandatory limit, esp when made for smaller riders.