You already answered 1 part of those reasons. Majority of those albums are simply PCM to DSD but done by the studio and deemed worthy by the studio.
Another reason is that the current DAC Sigma-Delta Chips are capable of upto 256x Over Sampling In conversion. DSD512 is Oversampling of 512X which is Twice as much than any desktop DAC-IC can do at the moment. But that is technically speaking. Sound performances, you will have to listen to it yourself.
One of the reason why many companies do not want DSD512 on Portable player is due to how much power it consumes and heat dissipation problems. It also needs very beefy clocking systems too. The DMP-Z1 from Sony will not enable this function either
Sorry but that's total BS .
You can't recreate / retrieve data that never existed.