OpEx means that if demand for your service goes down, cost goes down, your hardware does not become a capital liability since it depreciate fast. Way easier to justify changes to it too, you don't need a purchase project to get new instances, you're already "approved" and the contract was already signed with fluctuating costs. Needs more hardware? press a button, no need to research vendors, get contract negotiations in place.

AWS makes the life of finance and leadership a lot easier because they spend a lot of money justifying their superiority in ways that you don't have to think too hard to use and be taken seriously. They're to CTOs what think tanks and lobbyist are for lawmakers.

"No one got fired for buying ibm" for the new era.

There is a lot of truth in AWS propaganda, they're great for many things. But some of it is built on lies, cost being one, performance another.