A. It is supremely surprising that this isn't already a legal requirement. My modest software hobby business is required to keep durable copies of all communication for several years, as has been the law for decades. Yet a commercial airliner responsible for the lives of possibly hundreds of people is permitted to trash it after two hours?

B. The storage costs of cockpit audio recordings of a jetliner for its entire service lifetime might be less than the fuel for a single long haul trip. Even if we add in overhead for redundant replication and other expenses. If money is the legitimate reason for hesitation then this is miserly on an extraordinary scale.