You're getting downvoted, but your answer is partially correct: when you're a small startup, it is almost certainly cheaper (in terms of time and operational complexity) to outsource infrastructure to the cloud.
However, once you hit significant scale, the lessons from the operational experience of all of the major firms have been pretty consistent: it's cheaper to operate your own data centers than it is to outsource them.
Depends on what you mean by scale. If scale means providing services globally to many jurisdictions, you're going to have to start doing the things that the big players so like putting data centers in specific geographies (e.g., EU, China). That means getting real estate, power etc. At that point I think the scale tips in the other direction where it's now more costly for you to "scale". So, cheap at the small end, cheap at the high end and expensive in the middle (cloud).
From the perspective of a Fortune (checks list) 15 company: AWS saves us a fortune. No facilities costs all over the world with power/real estate/lawyers to handle local laws. No data center engineers across the globe. A solid discount on list. Consistent bills (thanks to judicious RI buys) and servers that are available in minutes - not weeks (have you ever seen enterprise IT ticketing practices?!)
If we had two orders of magnitude fewer employees/servers/locations AWS wouldn't make sense. But at this scale nothing else makes sense.
If you have reserved instance style workloads and aws is saving you money, it sounds like your private data centers were just grossly mismanaged or you have a negligible compute load.
AWS was likely just a way to overhaul inefficiencies in a legacy IT org. Someone will be able to do the same thing in 5 years moving you from AWS back to self-hosted.
People really need to stop. There is no Fortune 15. I get that your e-peen needs all the help it can get, but this is like a grown adult giving their age as 41 "and 3 quarters".
Speaking as the chief architect for solutions that are deployed on the cloud for financial services, this is not true. There is a point at which the infrastructure to manage the infrastructure becomes more expensive than the hardware and the network. Regulatory compliance especially PCI and HIPAA become very difficult to manage. Downtimes percent risks to large strategic customers. At that point the cloud comes in to atone because of the ability to scale completely dynamically and the capability for automation.
Sounds like you're either not that big or you have an incompetent team. If you have PCI/HIPAA/whatever under control, it doesn't magically get harder as you get bigger. Outsourcing it just means you pay someone else to get it right, in addition to giving up control.
However, once you hit significant scale, the lessons from the operational experience of all of the major firms have been pretty consistent: it's cheaper to operate your own data centers than it is to outsource them.