I'm curious too! And I also agree that semver in _most_ languages is a mess.
I'm sure someone could build a semver-checker for Python or JS or Java or whatever, and I'd even be willing to help them and walk them through how cargo-semver-checks works. But in Rust, a big driver of adoption is that Rust and cargo are opinionated about things, so people adopt cargo-semver-checks not necessarily out of love for semver but out of a desire to not wake up to 100 people being upset in their GitHub issues about broken builds. The adoption situation might be harder for other languages with less opinionated versioning stories.
I'm sure someone could build a semver-checker for Python or JS or Java or whatever, and I'd even be willing to help them and walk them through how cargo-semver-checks works. But in Rust, a big driver of adoption is that Rust and cargo are opinionated about things, so people adopt cargo-semver-checks not necessarily out of love for semver but out of a desire to not wake up to 100 people being upset in their GitHub issues about broken builds. The adoption situation might be harder for other languages with less opinionated versioning stories.