The problem is that the two work hand-in-hand, thanks to the advertising driven search model, and the search engines owning the main advertising platforms.
It should be easy for search engines to identify an original site from the SEO spammer rip-offs - the original site is going to have no adverts (or certainly fewer) while the SEO spammer copies are going to be covered in adverts. The problem is that the search engines have no incentive to do so, in fact if anything they have the incentive to send people to the sites with more adverts.
And of course the whole problem has been created by the search engines in the first place - there would be no point in SEO spammers making advert-laden ripoff sites if it wasn't to rake in advertising revenue.