Too much was spent on salaries and benefits. Only a month or two worth of cash was kept in the company to handle expenses. Free cash flow was pulled out of the company while it was still a viable growth opportunity. All the warning signs were ignored despite a vast majority of their revenue coming from a single source. Most egregiously, even though their traffic cratered after Google's Panda update in November 2012, they didn't reach out to the head of the web spam team at Google because... they didn't want to bother him.
Still, it's hard to admit mistakes. I have enormous respect for anyone willing to share their experience like this.