Blame the economy.
In addition to Elizabeth Edwards, the source (National Enquirer), and plain old bias, add economic hardship to the list of reasons the MSM failed to investigate the Edwards scandal.
Howard Kurtz, in his "Media Notes" column surveyed the scene surrounding the deafening silence of the media gatekeepers:
By early last week, journalists were in the awkward position of refusing to report on explosive allegations that were almost certain to knock the former North Carolina senator out of the Democratic convention. They were in a box of their own making, one that came to feel airtight and uncomfortable.
When critics, especially on the right, accused the media of protecting a Democrat because of liberal bias, journalists were unable to respond, because to do so would be to acknowledge the very thing they were declining to report.