OP explicitly talks about the system interfaces - i.e. the kernel. I don't see any sign that they are talking about the whole OS. In fact, if they were talking about the whole OS, the post would be nonsensical: any OS has a userspace implemented in some language, so any OS is 'pushing a language' in this limited sense, by definition.

Either way, the OP is clearly confused about what Linux-the-kernel provides vs Linux-the-OS. Their example of async IO is nonsense - async IO is built into the kernel itself, as are threads (which are not even available in libc, at least until very recently).

I will admit that I was "greatly exaggerating" (read: lying) when claiming that kernel maintainers don't know/care how libc uses their API. But the point is that, while the needs of libc obviously inform their designs, they are not directly writing or maintaining it, unlike virtually all other mainstream OSs.