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This has been explained so much that there is a documentation page all about it: https://www.kernel.org/doc/html/latest/process/stable-api-nonsense.html https:/

• g_p 6y ago
  Good link - there's also a clear case that "requiring" the kernel to provide long-term stable driver API/ABIs is simply reallocating a cost towards the benevolent open source maintainers, to allow closed-source companies "leeching" (to use Greg K-H's words) from the kernel devs to benefit. There's clearly a non-zero (and indeed non-trivial) cost to providing a stable kernel driver API, and the kernel devs don't want to bear that cost, as they feel it would hold back the kernel from evolving, improving on APIs, and fixing security issues or other implementation bugs. The other side of the coin is that closed driver developers want this stable API to reduce their own development costs, but they will not follow the "intended" workflow that reduces the ongoing maintenance cost to effectively zero.