The explanation is quite simple:
As the FO pool dries out because the T&Cs are now known to be crap and the AAR intimidation campaign leaves its stinkin' marks, and only the desperate and unemployed FOs apply, but the company desperately needs more pilots, they look for DECs. There are much more on the market, especially those stuck on single aisle jets for another century. The shiny twin aisles at EK have a huge appeal and the pprune-deaf and blind join. FOs at EK get pi$$ed due to their being stuck on the right seat, they leave, making the hole on the right even bigger. Upgrades are therefore not possible, and even more DECs are necessary.
I predict a wave of downgradings in the near future. If you consider the complete bs punishment mentality setting in (the last couple of buddies I flew with, right or left, have almost ALL had some sort of warning on their record, for the very slightest little bs they can come up with), it is obvious that the ever more lacking numbers on the rhs will be filled with disciplined captains. Clever, clever! Watch your back now.