They do get prosecuted. Except they carry so much legal firepower, and then hide behind complexity at a level where the govt. has to consider which cases to go after.

See the sec going after goldman for example.

Further, the govt in many cases has been co-opted or convinced that should they go after these guys, the economy would collapse. I believe the state wide cases against the mortgage companies foreclosure mills was a close example.

I don't have the details on the tip of my fingers anymore, but in essence the mills were getting sued in every state, and were negotiating.. Perhaps to get the suits bundled together I think. At which point they introduced a clause which stated that they would not be sued for anything else after this case, on this matter.

Essentially protecting them from further prosecution/investigation. If it weren't for a handful of DAs who said no, particularly the NY DA office, it would have passed.

And then there's regulatory capture and resources being reduced to investigative bodies.

I used to follow this mess for a while, and there are a lot of prosecutions and maneuvers and counter maneuvers going on.

If you are wondering why they aren't being sued I suggest doing some research, rollingstone alone will have some great articles, and if you would like the big picture blog, carries some old articles, and is always tracking the crap the finance industry is pulling.

There is a lot going on - make no mistake. It's just that the govt really is the underdog, and is sadly the first one to get bashed on HN.