Both power supplies are mass produced, they seem to be OEM by Delta.
The choice of an external power supply at this power level must be more expensive. It needs a power cable and connector, additional case and fan, and if you look at the XB1 board, there's a ton of additional power regulation necessary because the power arrives very dirty and cannot handle quick transients. That is not the case with the PS4, power arrives clean and you can see the motherboard have nothing there, the 12V goes directly to each VRMs.
I would even conjecture that the weird mess under the SoC is somehow related to the power being external and so difficult to clean up. But that's a wild guess.
And as I said previously the extra shipping cost (more packaging, more weight, bigger box etc)