And the VRMs and associated circuitry are the most likely thing to die on the motherboard. The PSU, at least in my experience, is the most likely thing to die i

And the VRMs and associated circuitry are the most likely thing to die on the motherboard. The PSU, at least in my experience, is the most likely thing to die in a desktop computer. So now you have all the most likely to die components on the most expensive part of your desktop system. Being able to replace the PSU without the cost of the mobo is great for human people. For corporate people and their economies of scale it makes less sense than just making everything 1 thing and throwing it out when it breaks.