During the era of OS X Snow Leopard (10.6) and Lion (10.7), installing macOS on a PC was not as simple as clicking "next" on a USB installer. The kernel—the core of the operating system—was often coded to look for specific Apple hardware signatures.

It supported the "vanilla" kernel, which allowed for official Apple software updates (up to version 10.6.4 or later) without breaking the system.

How to Install Mac OS X Snow Leopard on VirtualBox - Sysprobs