Except that the Windows applications that do use syscalls directly (i.e. anti-cheat software) are intended to break when something changes. It's part of their w

Except that the Windows applications that do use syscalls directly (i.e. anti-cheat software) are intended to break when something changes. It's part of their way of defending against tampering. It's also part of why they need to be continually updated and why some old games won't work at all on newer OSes until a patch is applied to hack out the anti-cheat engine. If syscalls were stable, they'd just try to use some other means to obfuscate their OS calls and ensure it's sufficiently fragile as to break easily if something changes. tl;dr the lack of stability is a feature not a bug for this use case.