Of course it doesn't provide backports by itself, it's a versioning system. But version number changes with SemVer are meant to indicate whether an update includes new fearhews or not (minor bump means new features, patch bump means bugfixes only).

Of course, the actual issue is that maintaining backports isn't free, so expecting it from random single-person projects is a little unrealistic. Bug fixes in new code often need to be rewritten to work on old code. I do maintain old release branches for some projects and backporting single patches can cause whole new bugs that were never present in the main branch quite easily.