I believe it's because Democrats have accepted the Republican playbook and offer no clear alternative.
Your district leans toward progressive politics. Mine, through the magic of gerrymandering barely is so. We have a large group of rural voters who are conservative. They want the federal government out of their lives. Regulations, they claim are killing their way of life and it's not completely false to say so. It is Wyden's job to represent all of his constituents, including the ones who didn't vote for him. He entreated people at a rally held recently to listen and talk to our neighbors about the issues without personalizing and especially without dismissing their complaints as ignorant. I'm trying to do that. As Wyden points out, a small shift in the vote would have put an (my words) obnoxious Republican in control of representing my district. In my district the issue isn't Democrats are same as Republican. Quite the opposite.
What I don't understand is why my rural neighbors would vote against the very same food stamp programs their kids depend upon. The thought experiment that I'm posing here is that my rural neighbors despise food stamps and want the kind of life they remember or their parents told them about when growing up. Back then, logging and log mills were a large part of the economy. Also, strawberries that were grown and processed in nearby processing plants were an important cash crop. This has gone by the wayside. In the face of this, they don't see liberal initiatives like universal healthcare, regulating Wall Street, clean water act as relevant. What does that have to do with the lack of jobs in their area?
This kerfluffle started when I said it was OK with me for a Blue Dog Democrat to vote for Rick Perry. In key areas like passage of an amendment to overturn the Citizen's United ruling, those same conservative Democrats voted with Sanders and others. They will oppose other causes important to their districts like regulations on farmers to protect waters from ag runoff pollution. Recall that most people are happy with their own congressmen. I may not agree with them on all issues but I agree that the people of their district have the right to vote for them. And they sure as hell are better than the Republicans they defeated.