Software generarated ID's are a function of the specific instance of the OS loaded on the PC, and alternatively one can change the OS or run multiple OS's on the same PC. Even MAC addresses can be changed by changing the network adapter or virtualizing the MAC address. IP addresses are easily changed.
In contrast, CPU ID's are hardcoded and permanent. As long as one has that PC they can be uniquely identified no matter where they are, no matter what network they use or what changes they make to the software. They are owned.