When marketing web sites on the internet 10 years ago, people “surfed” the web, clicking on links between sites they already knew about, links from directories and review sites. Search engines like AltaVista, Lycos, Hotbot, Excite, etc were around as well. Remember those?
People like Eric Ward pioneerd the practice of promoting web sites editorially resulting in links from these sorts of resources. Links had to come from relevant sources otherwise the traffic was irrelevant.
Google came on the scene with PageRank and boosted the value of bot detected links. Search engine quality improved substantially but opportunistic webmasters and eventually SEOs, identified and took advantage of as many methods of link acquisition as possible. Many of those links being topically relevant and many completely out of context. Think “link farm”.