It could be a supplier switch; ex. Ford sources part from Acme widgets. Acme underbid the contract and after delivering the initial batch, tries to renegotiate, Ford says “F.U. more than one oil pan supplier in the world”, they land a contract with Wile E Coyote creations who can make the pan to spec and do it cheaper. Because they’re using a less pliable plastic. Initial run of ’17’s work, but the WEC batch immediately show problems. Now, only the bad pans are in inventory. Ford goes back to Acme, hat in hand and pays exorbitantly for warranty pans. Now they start seeing a much smaller percentage of the first Acme pans failing. Ford say “enough of this, begone with your plastic for oil pans”. they source a metal pan from heavy metal and don’t look back.
But, what do they do with all the Acme and WEC pans? WARRANTY!
about 7 or 8 years back, Ascerbis replaced a few truckloads full of fuel tanks for Ducati, Husky, Aprilia, and many more. The problem was the US fuel blends were causing warpage of the plastic. In some cases the warpage was bad enough that the tank couldn’t be removed without breaking the mount points. Mine was only cosmetically affected but got replaced on my Ducati. The same tank worked in every other market, it was only the US fuel blends that were the problem. The replacement was - wait for it.... Plastic.
I can see several ways in which Ford would have had this issue with the oil pans. I’m sure the metal pan is more expensive.