The ratings agencies that were giving AAA ratings to financial instruments that were built on lies and fraud just because there were very big deserve some scrutiny. It's hard to believe that the entire industry was incompetent and that none of them were colluding with the people offering those instruments.
So yes, the ratings agencies may have been cheating, but they are not remotely 'bankers'.
And it's 'very easy to believe' why they did it - because ratings are their source of income. If they don't play nice, banks go elsewhere.
Similarly 'Gartner' and other such entities: you don't buy their reports, you may not get in the 'magic quadrant'. No 'collusion' is needed, just a brain.
But this misses the question again: what did these banking execs do that was illegal? What should they be prosecuted for?
There's just not much there.
The system relies on Credit - if one part of the system goes down, it can take the rest with it. It's not entirely irrational that one bank goes down - the risk of course is the collateral damage.
The 2008 crises was a systematic failure of lack of oversight, greed, stupidity and some bad actors, mostly not illegal activity.
If you think someone should be prosecuted, then tell us who they are and what crimes they have committed, instead of resorting to crude populism.
Better yet, try to understand what actually happened.