Different types of these strategies have been around since before google existed. Hell, even web directories (like early yahoo!) had to deal with spam, early google had to deal with keyword spam. Paid backlinks, spammed comment sections with backlinks, copied content sites as backlink farms, all of this existed at least as early as 2005-ish. For some sites (some of them with legitimate info) the meta keywords tag (even though google stopped using it very early) was the bulk of their size for just this reason.

What has so radically changed the last couple of years to make spam take top spots on the SERP?