Because Audi views themselves as a performance brand over a luxury brand. They're also hungrier and thus more responsive to consumer demand.
BMW allows carplay with a monthly subscription to the rest of their services, largely because they believe that as long as you're getting the full benefit of a connected car, you'll be attached to the value - strategically, it makes no sense for them to give it away from free.
The other thing? These companies are starting to change their mind as consumers demand it as a feature.
