AWS is more of a commodity, right? You use it for compute and storage and networking, but how much of what you write is intrinsically tied to AWS? With what we're talking about here, there's a language and a bunch of libraries where, if the company decides to change things, your code stops working, and there's no way to make your code work again without rewriting some arbitrary amount of that code. Maybe the company decides that a whole kind of activity is now bad, and you can't do it at all on their platform.
With AWS, you can pack up and go to a different cloud provider, and get the same Linux and the same gcc and the same TCP/IP stack. There's probably some other code you'd have to change, but the essential core is non-proprietary and nobody can take it away from you. Abstracting further, if Linux decided to go in a weird direction, you can get a POSIX-conformant Unix-like OS from other groups, like FreeBSD or Illumos. The Linux codebase can be forked as well, providing an even stronger insurance relative to what happens when some company's or business unit's incentives no longer align with yours.
And that part about aligning incentives is powerful. In the closed-source world, it's also fragile: One company being bought out can shift things tectonically for all of the software that company made. It becomes a treadmill, or a movie routine of constantly jumping from platform to platform as each of them dies off or is pulled out from under you as "corporate synergy" realigns strategic chakras feng shuis your old codebase into worthlessness.