Getting petabytes of storage isn't the problem, transferring the data back and forth is.
Taking a full month to recover a downed social media platform isn't really acceptable, but it's still better than being literally unable to recover it at all. Spending a small fortune to ship hardware to an AWS datacenter and convincing/paying them to load it directly would probably also be worthwhile, when we're talking about simply losing a $500M company. If the claim here about "no backup" is true, it's so profoundly stupid that everything I know about best practices sort of goes out the window. Approaches that any sensible person would consider unacceptably slow and unreliable are still a step up from a completely blank playbook.
(I guess the theory might be that Tumblr is such a trashfire it can't be restored, or would lose so much value in days/weeks of downtime that there's no point in even planning for that. Again, I don't really know how you run cost-benefit analyses when it's not entirely clear the project has benefits.)
That's not even talking about availability, as you are now getting into the realm where it starts to get questionable whether even Amazon has enough backhaul capacity available at those locations so that you can actually max out 50+ 10Gb connections simultaneously.