"There's no reason why so many deep blue states should be electing so many corporatist ConservaDems."
It's called money.
In my own district a few years ago, Jared Huffman (not yet an incumbent) ran a well-financed campaign against the farther left and ideologically much closer fit to this district (one of the most progressive districts in the nation) Norman Solomon. Huffman got the slick mailers in every mailbox, the fancy signs posted everywhere, the endorsement of the local newspapers (they aren't really local, they're owned by the same giant media conglomerates), and what little T.V. time there was. Solomon had a lot of very enthusiastic volunteers backing him, doing grass-roots organizing, knocking on doors, but in the end, with a great candidate, an extremely progressive electorate, and energized support, the progressive candidate lost handily to the fauxgressive Huffman.
Huffman isn't the devil, but this district is way farther left than him, and we had a rare and excellent candidate who was unable to overcome the obstacles of money and corporate institutional support.
Our real challenge is to learn to defeat money with progressive values. Bernie's campaign is a great attempt at this. We have to stigmatize candidates accepting corporate money, and not support them, or we'll never get anywhere. Defeating money is really hard, not impossible but unless we as a constituency swear off corporate politicians, we will continue to get our asses handed to us, and our jobs handed to the most desperate and least regulated labor forces on the planet.