The Principal PM in charge of the "regionalization" effort was asked in a Q&A "why didn't we just switch to IPv6?".
Her answer was something along the lines of "The number of internal networking devices we currently have that cannot support IPv6 is so large that to replace them we would have needed to buy nearly the entire world's yearly output of those devices, and then install them all."[0]
It's easy to presume malicious intent on the IPv4 front from Amazon, but with so many AWS systems being on the scale they are at, I find it easy to believe that replacing all of the old network hardware may just be a project too large to do on a short timescale.
[0] - At least, that's my memory of it. I'm sure that's not an entirely accurate quotation.
There is no reason any company of any size should run out of IPv4 addresses internally, IF they are doing proper IP management. If I were to wager a guess I'd say there was a lot of waste going on, issuing /24s or larger to teams when all they need are /29s etc. It adds up over time. Once they exhaust private IP space they can always buy more at auction. They are Amazon after all, there's no shortage of money. This is just mismanagement of resources.
Do you really think someone intent on killing himself will look at a blister pack and think, "You know, if this was in a bottle I'd go through with it, but this doesn't seem worth it, it's way too much work to take me own life"?