From an outside nerdy perspective, I find it interesting that airlines like Aerolineas Argentinas, Tanzania Airlines, Air Canada, and many others outside of the US who have either never operated their own pure-cargo flights or haven't done so since the 707 days are entering the business, as in doing so in an on-going fashion with new announcement multiple times per month, while suddenly FedEx\UPS can't justify the MD-11s and their current mass. Sounds more like they can't make record profits at that mass and want to offer something more consistent. It seems like FedEx, UPS, Amazon, and other US companies are having major issues but cargo is still expanding almost everywhere else...
I'd imagine staying big is a good deterrent against Amazon's growing fleet(s) as well, but I suppose they may just be preparing to see more UPS/FedEx/DHL mass shift to Amazon and "right-sizing" ops for that future?