Is very simple
The fact new 4k boxes have a relatively powerful CPU means nothing regarding what the firmware have access to.
If there is a DES decoder and you cannot access it,is the same as no decoder at all.
When they sell the chip,there is an understanding about its use.And there are licenses to pay depending on its use.
Everyone pays for a CSA decoder since is mostly a standard,but as DES is not,think about which companies use DES : directv,powervu.....and you might not think on any other.....
It took a while for Oscam to find access to DES decoder in dreambox,other boxes might never do.