SEO practices at the time focused on content optimized around keywords and anchors, exact-match domains, massive networks of linked sites, and, towards the end of the phase, highly curated content .

Towards the end of the Big Box era, Google specifically tried to turn away from companies that relied on then-standard SEO practices and introduced a penalty for over-optimizing a page in May 2012. Excerpt from an interview with Matt Cutts:
The idea is to try to level the playing field a little bit. By comparing all of these people who were kind of, for lack of a better word, "over-optimizing" or "over-doing" their SEO, to those who are creating great content and trying to create a fantastic site, we want to level the playing field that they're on.
Google was clearly aware of the problems, but of course the SEO specialists immediately reverted the changes and reduced the level of optimization of their pages and thus lowered the level of the recently developed area. This heralded Phase III.