And why did they (in your opinion since nothing is official) disregard SOPs? Probably they got up that morning and said over coffee, hey guys, let's just disregard all that SOP stuff and see what happens. There is a reason why SOPs during normal ops are disregarded or not done. Find out those reasons and perhaps you are your way to understanding the accident. Oh so easy to say, bad pilots, goodby pilots, problem solved. Oh and let's throw in some more SOPs for everyone to cover our a**.
Alot of factors may have been involved, confirmation bias, fatigue, rostering, distractions just to name a few. The holes lined up nicely. But saying simply a disregarding of SOPs was the cause, you are lineing up with manufacturers, managment and lawyers and investigating the accident as was done in the 60s and 70s. Find the "pilot error" and problem solved; investigation over. Just work your way backward from the accident/incident to where the pilot error is obvious and then problem solved. Try a new approach, work your way forward as if you are in the pilots' position to where the mistake materialises and, ureka, you may come to understand the event and prevent a similar event in the future.
Look up the definition of the word "accident" and it may help an investigation. A willful disregard of SOPs (too many SOPs, too many not making sense, SOPs that actually cause distractions themselves) does not constitue the definition of the word... accident.