Why aren't the CVR and FDR required to store data for a longer period? I'll be honest I don't know a lot about the brand new airplanes, but one think I do recall a lot of from reading accident reports is that they typically only recorded the last 30 minutes of data.

When an aircraft costs over 30 million USD, with some costing in excess or $300 million, surely being able to increase the amount of data recorded 10x or 20x pales in comparison to the costs?
CVRs typically store two hours of voice recordings (source). 

It simply wouldn't serve any purpose to store longer recordings.
It is extremely rare for an emergency to last for such an extended time.
Qantas 32 was one of the longest emergencies in recent memory, and it was only 1:45.

The MH370 flight was longer, of course, but it still hasn't been recovered.

While I'm sure it is technologically possible to record more voice data, that would primarily record innocuous and routine conversations among the pilots.  

I suspect that the pilots, and their unions, are reluctant to have their mundane and irrelevant conversations recorded and inspected.