It kinda sounds like you think that Google doesn't have the resources to have a human decide that stackoverflow isn't itself a spam clone.
This is a huge problem for a very small number of sites and a non-existent problem for everything else. The list of authoritative, egregiously-copied sources could easily be maintained by one person. The only difficulty comes from determining when to trigger the system.
They have the resources, they don’t have the willingness. Google’s MO is never hiring a human to do a job well, when a computer can do the same job badly.
This is a huge problem for a very small number of sites and a non-existent problem for everything else. The list of authoritative, egregiously-copied sources could easily be maintained by one person. The only difficulty comes from determining when to trigger the system.