As far as the user is concerned it is "Linux", when people say they use "Linux" they do not just mean the kernel, they mean the entire OS.

On Windows these libraries have APIs that remain backwards compatible (new methods can be exposed, but existing stuff remains there). Unless the equivalent Linux libraries also decide to provide backwards compatibility, they'll just make Linux look broken (even if it isn't the kernel's fault).

(and no, this isn't something you solve by being pedantic about what is userspace and what is kernelspace and who controls what, as that information doesn't solve the actual problem - you solve it by cultivating a culture that actually cares about backwards compatibility)