It's that simple. Voters don't actually care, it's just another weapon for the establishment to use against outsider candidates.

They'll prop up a thousand Bidens and Cuomos and Weiners and Swallwells for years because the establishment doesn't actually care either. They'll disappear Al Franken when all they have is a pic of him doing hover hands over a plate carrier so they could repeal Dodd-Frank or Eric Massa for tickling a male staffer so they can pass Obamacare instead of single-payer.

If you're challenging the establishment in any way, you just have to be Mr. Rogers tier squeaky clean.