You can't rely on their goodwill, you either make it enforceable with a license, or you just treat it as a something that you don't expect to make money from.

The comparison to artists doesn't really hold, because they won't start a work for someone without them asking, then showing off their creation and hoping that the involuntary "client" will pay for it once it's already been done.
While programmers can be commissioned to make some piece of software, that will most likely end up as proprietary, unless stated otherwise in the contract between the two parties, akin to a commissioned piece of art, hardly any client will be ok or even proactively ask you to release the work under a CC license.

Companies especially are more revenue than image driven (or solely tbh), so they won't "waste" any money where they can avoid it, if Amazon finds a nice service they can host and tweak on their AWS that promises to be useful and make them lots of money, they will just go for it and stay within the lines of what the license allows, which often is "too open" for its own good (think MIT), so the project won't see nothing like a contribution back, let alone money.
The illuminated companies that can (more like want to) afford to contribute in any way to software they rely on are few and far apart and it takes them to realize how much of an impact the project they're using makes on their business, which is often difficult to put into tangible numbers, we see that happening mostly with the biggest projects, think Blender, Linux, etc. The poor library developer will most likely never see a dime coming from the thousands of employers whose developers will pull in their dependency for their product