The problem is that most of the data they seized is non-infringing. MU had something on the order of 19 petabytes; a fraction of that is actually "evidence", the rest just went along for the ride.
Perhaps, but how does evidence handling work when it's of crucial importance for the defense?
This isn't actually related to the defense, it is for a random Megaupload customer.
The defense cannot get the data, either.
They don't want their files back, they just want the FBI share them. ;)