I don't think using GPL is a good way to try to make projects sustainable in most cases. It doesn't even require that companies make the sources for their modifications and other derivative works available to the public if they don't publicly distribute the software based on it.
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The reasoning and purpose behind it is giving users the ability to modify their software. It's what it was designed to do and it's reasonably effective at achieving it when software is publicly available and used by a substantial community including developers to use the sources.
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I know that too. It’s often not sufficient. It was a random idea to turn some ever pissy corporations to maybe contribute to a community in other ways than using them as a free lunch by playing on their fears of having their lawyers look at licenses.
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Companies like Amazon and Google are smart enough to understand the licenses and know that they don't need to contribute anything back or pay for a license though. I guess providing a license can work in some weird cases like the useless $6000 SQLite license that's available.
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Apple flat out bans GPL anything for example. They’re a big company that’d rather not bother at all. Smaller companies also frequently have the same kind of approach. I’ve worked for a few of them too.
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In the Apple case, I think it's really the other way around. In the past, they incorporated tons of GPL2 software and released some of their own. It's the GPL3 that they're allergic to, maybe due to the patent grant but it also directly forbids having an immutable root of trust.
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It's GPL3 that bans using the software as part of firmware or an OS with signature verification based on an immutable key in hardware. Apple couldn't have used it on the iPhone unless they supported users setting the key like many other devices. Patent grant may also scare them.
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If someone is using GPL3 because they believe in the ideology behind it, then I don't think they would want to sell a license for creating a locked down device. You could use GPL3 to force companies to pay for a license for this case, but it's a tiny subset of commercial use.
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It also shows something quite revealing about the GPL and the standards for open source and free software licenses. That part of GPL3 is incompatible with the GPL2, and was considered non-free until *they* did it. The decision on whether a restriction is non-free is subjective.
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It's not, and it's also a hidden requirement of GPLv2 if the FSF hadn't sabotaged interpretation of it. Since the final signed work is derived from the signing key, and that key is needed to make use of mods, it's part of the source ("preferred form for modification").
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If that was really the case, it would have implications far beyond forbidding a locked down system like iOS where the OS verification is chained from an immutable root of trust rather than one the user would control. It was never even the FSF interpretation of the GPL2 license.