What do you mean not mature? This has been on the market in cars since the sixties. Audi has had it in their top models for over a decade. It's just expensive
A quick search for "CVT reliability" produces pages of horror stories related to the Audi (and other) CVTs.
The CVT is only available on the A4 and A6 (not the A3, A5, A7, A8, Q5, Q7, et al). Also, the CVT is only available with the smaller engine options. Finally, the CVT cars are front wheel drive only, no quattro available.
They're an option on the more expensive Audis and a few other manufacturers have them.