It's because of how much the Clinton(s) are hated by the right. Pathological hatred* makes it likely you will believe the worst regardless of evidence.
And thus the flip side is also true. There were such obvious witch-hunts from the right that large parts of the left rallied around to them. Which meant that things that would have been scandalous for anyone else aren't taken seriously.
Take
Juanitta Broadrick. Look at that link and tell me what the reaction would be to it if those allegations were against any other person. Specifically, what Gloria Steinem or any credible feminist would say about the alleged rapist and his wife who allegedly told the victim to keep quiet.
For an idea of how far this goes, to impeach Clinton for lying about a BJ was just ridiculous. But prominent people had closed ranks so tight around the Clintons, a
feminist publicly said Monica Lewinsky should start renting out her mouth to the highest bidder as a future career.
Then look at her email scandal. For 5 years the right has been chasing the ghost of Benghazi, where she allegedly didn't save an ambassadors life or lied about who killed him (their allegation keeps shifting). In the course of that they stumbled onto the email scandal, where she violated rules she herself set up about secure communications. But they kept hammering away at Benghazi, and for a long while talking about emails was as taboo as talking about Benghazi (Bernie in the debates, when asked to attack her on that: "The American people are sick of hearing about your damn emails, let's debate policy")
The GOP grilled her when she was appointed SoS about potential conflicts of interest with her work and the Clinton Foundation. The Foundation has been getting money from foreign governments she was dealing with directly as SoS, including authoritarian regimes, and with high-profile companies with whom she was working (for example the banks that were financing the Keystone XL pipeline). It just so happened that the bank donated to the Foundation around the time she expressed positive sentiments about the pipeline. And in another coincidence the Foundation would get money from a foreign government and around the same time the US would approve arm sales.
*And the more I read about them the more pathological is my hatred toward them.
