Why in the world did anyone ever consider Text Link Ads (TLA) as a legitimate form of building links?
Because way back in the day before Google existed, people bought links. There were no search engines to manipulate, so we bought links on relevant sites in order to steer our target audience to our sites - there was no other way to do it. Then Google took over, and suddenly links had a whole new meaning. But if you weren't following SEO, you didn't know that, and you just thought link sales were still alive and well.