The C and C++ specs are full of UB though, more like a "minimum common denominator" for compiler devs than a strict spec that users can rely on. It's way too easy to write spec-abiding code that behaves differently with different compilers/architectures/optimizations.

Specs are definitely a good thing to have, but often they're just brandished as a bullet point without looking at the details: how good is the spec, what does it add over the existing tests/CI/RFCs/proofs, etc.