One key difference is that the equivalent to kernel syscalls on *nix generally involves userland-provided services, and this applies to a lot more than just ordinary file access. The local equivalents to arbitrary "containerization/namespacing" and "sandboxing" are just natively available and inherent to how the system works. You can't do this out of the box on *nix where every syscall directly involves kernel facilities, so the kernel must have special provisions to containerize, sandbox, delegate specific things to userland services etc.
One key difference is that the equivalent to kernel syscalls on *nix generally involves userland-provided services, and this applies to a lot more than just ordinary file access. The local equivalents to arbitrary "containerization/namespacing" and "sandboxing" are just natively available and inherent to how the system works. You can't do this out of the box on *nix where every syscall directly involves kernel facilities, so the kernel must have special provisions to containerize, sandbox, delegate specific things to userland services etc.