Mind that if you'd ever wanted to integrate again, this means buying land, planning infrastructure, building it, planning, obtaining and setting up hardware and software, hiring, training, defining and testing procedures, etc, as you're starting from zero again – and all this while the costs, which forced you to consider this move, are piling up. Odds are, you'll never do this and cloud providers will know this. The comparative costs are now not those of running your own infrastructure, but those of setting it up (again).
FedEx had very few on site people managing the hardware, it seemed like most work on hardware was done by the suppliers. There were also very few servers there and actually running, I think the software powering the enterprise took up a lot less than they expected.
Either way, I think you're spot on with the "training" part. FedEx was one of the first companies to raise significant capital and pursue a business dependent on technology. It also treated its people very well so relatively few left since the 70's. I think they just didn't train the next generation enough and they realized that those skills are disappearing rapidly because no college grads want to learn old & boring stuff and everyone who does know it costs a lot to keep (FedEx still heavily relied on COBOL when I left ~5yrs ago).
