Great question. If we look at 14 CFR § 91.609 (Flight data recorders and cockpit voice recorders.) I believe we will see that there is no requirement by the DOT/FAA for recorders to stream/upload data anywhere. Also, paragraph i subsection 2 only requires recorders to retain a minimum of 2 hours of recorded information.

Additionally, if we look at paragraph g we will see this: "In the event of an accident or occurrence requiring immediate notification to the National Transportation Safety Board...that results in the termination of the flight, any operator who has installed approved flight recorders and approved cockpit voice recorders shall keep the recorded information for at least 60 days". So it seems that since the flight was not terminated that a backup of the recorder data was not required to be made.

Money. Certifying a system like that would cost a fortune and unless the operator is forced to do it or you give them a very compelling case that helps their profitability, it ain’t happening

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.