It's the same reason that you never see the press mention congress's role in the subprime meltdown.
Politicians that are liked by the media say "Bankers! Wall Street!". That's what gets shown on the nightly news and repeated. Most voters don't care to dig further. Partly because the truth is more complicated. Partly because it causes cognitive dissonance to think contrarily to the narrative being told in the media. Mostly because looking into details would take people away from Monday Night Football, American Idol, and Dancing with the Stars.
As one who works "on Wall Street" (remotely) I can assure you that we caused the financial crash deliberately. I personally spent a lot of time working on it and I am now back at it again! You just wait 10 years for the next cycle!