Whether you're using Linux, macOS, or BSD, OS-packaged language runtimes exist for the OS itself to use, in OS-internal scripts and underpinning OS services. They shouldn't be considered "part of" the userland; as this invites userland applications to rely on them. These runtimes are actually something more like an "implementation detail" of the OS — the kind of thing whose binaries should live in $PREFIX/libexec rather than $PREFIX/bin.
(Mind you, if you're a system software developer, whose software gets packaged into Operating Systems, then you do have to rely on this "implementation detail." Which often means targeting very old versions of runtimes and libraries, compared to the versions that application developers get to target.)
Also, of course, there are "standard" language runtimes that should be part of the userland — e.g. /bin/sh. But these are literally standard — i.e. part of some standard like POSIX, that an OS can be tested for conformance against. Which is important, because it means that developers can write to a stable target of "POSIX compatible", assuming the existence of (and particular stable semantics of) particular standard runtimes.
But none of the "modern" language runtimes are part of any such standard. The version OSes ship should be assumed to not exist. (And major third-party applications do already do the right thing, in not making any assumptions of existence, but rather installing their own vendored versions of the runtimes that they can upgrade as needed.)