As others have chimed in, while working extremely well for _libraries_, which I believe Semantic Versioning was really proposed for in the first place anyways, it does not work or necessarily make sense for Kernels which are kind of a very special kind of library.

Once matured, kernels tend to never break backwards compatibility (or try very hard not to), and rarely track bug fixes with individual numbering. Often many changes are lumped into a single version update, because so many changes are already happening across many different subsystems.

I suppose also, now that I think about it, Semantic Versioning works much better for smaller scoped and smaller scale projects (like well scoped and designed libraries). The kernel is such a large piece of software almost like a collection of libraries hidden behind a single set of matures APIs that incrementing counters for every bug fix or tiny change doesn't make sense---and as has been established, major numbers would just never bump.