>Perhaps that's more of a cautionary tale for new projects than a justification for the expense though.
You can find case studies for both positions:
- migrate to AWS to save money: Netflix, Guardian newspaper [1]
- migrate away from AWS to save money: E.g. Dropbox [2]
A lot of companies (especially non-tech businesses) don't have the technical skills to run internal datacenters at the same competency as AWS. Thus, they don't want to be "locked in" to their own IT department that's slow and handicaps their business.
Dropbox, Facebook, and Walmart would among the very few that can competently run their own datacenters with advanced services like AWS.
[1] https://web.archive.org/web/20160319022029/https://www.compu...
[2] https://www.google.com/search?q=dropbox+migrates+off+aws+sav...