For all of those you would need definitive proof that those decisions were made with criminal intent to commit fraud. That is a very high evidentiary standard to clear, which is why these cases are so hard to prosecute.
Even the Enron case, which was a pretty clear case of fraud, took the government 5 years to build a case and win in court.
So, while all of those things you mention do indeed sound bad, they are incredibly difficult to prove in a criminal trial.
While I don't disagree with your points, it boils down to a defense by the persons accused of "We, titans of industry of finance, were so clueless, inept and incompetent that this unexpected thing happened. We definitely weren't intentionally trying to defraud anyone!". Doesn't exactly sound like a ringing endorsement for people whose yearly salaries are >$500,000.
Making profits unethically doesn't necessarily mean it's fraud. The two things are very different.
I can knowingly sell you a crappy car, and if you sign an agreement that you bought and accepted the good in its current state, that's that. Yes, I acted unethically, but I didn't defraud you.
First, that's not the defense. The defense is that the 2007-2009 recession was a "black swan" event resulting from a confluence of factors that nobody expected. To date, I'm not aware of any economic work that points, with 95%+ certainty, to a specific cause of the recession.
Second, a successful prosecution requires proof beyond a reasonable doubt that a specific person performed each element of specific crimes. Defendants do not need to even present a defense--and in fact sometimes do not, relying entirely on poking holes in the government's case.
