If I had 1-10 PB to move I could totally see most people using FedEx to ship JBODs around. For small transfers it makes sense, and we also have a product for this. Internally I'd use our WAN for those, which is where this now starts to make sense: Amazon does not have anywhere near the global WAN capacity that we do, nor so far have they had a good reason to have that capacity.
If you've got the global capacity to allow a customer to peer to your nearest location (and your nearest location likely isn't too far away for most of the world), fiber makes sense for large (~EB-scale, which I assume anyone with 100PB+ is well on their way to 1EB+) amounts of data. We have a product for these peerings (primarily for customers in colos): https://cloud.google.com/interconnect/docs/concepts/dedicate...