Is there some sort of underground competition, for whomever can build the cheapest PC? Why would you replace a UEFI 1150 mobo with a non-UEFI 775 board? The pre-installed OS probably won't even boot on the older board.
Edit: Or do you run a desktop PC parts chop-shop? Someone comes in looking for a shiny new 1150 PC, and they walk out with a re-formatted Dell with a 775 mobo? And the 1150 mobo / CPU gets sold on ebay? Because you've alluded to doing such things in the past (buying i7-4790 rigs new at Costco, and selling the CPUs, and replacing them with lesser ones), and I could never quite figure out the why.