Ok, I'll bite. I'm not pro hillary, but I will probably vote for her, because she is pragmatic, and has the best chance to win the GE, and keep the right wing loonies out of the house. Its not that hard to understand the argument, so I will try.
First you need to realize that Americans is not far left. Its actually more center-left/center right depending on the state. Bernie is too far left for most americans. They can't relate to his message. They can't see him winning the GE. The recent polls show this. Every poll shows this. Most americans don't even like his policies because it sounds too good to be true, so we know its just empty promises. And we know its impossible for him to deliver on. We've seen it before. Ted Kennedy had similar ideas decades ago, and ran on similar policies. They can't win. The last 50 years have shown us that far left liberal senators cannot win. So what makes Bernie different?
We see him having a coalition of youth under 29 (that mostly undervote/ don't show up anyways) and white males. Thats it. Meanwhile he is getting demolished in black votes 9-to-1, hispanics and asian votes 3-to-1, and losing female votes 3-1 in most states. Blacks and hispanics don't support him, as they dont see how he benefits them, or what he has done to prove trustworthy to their cause. He'll never get their vote.
As a generally well educated person that understands politics, we understand how the government works. Its two party system is setup to not allow changes to happen quickly. The founding fathers made is that way on purpose so that drastic changes/populist appeals/emotions do not become law. Everything has to be fought hard for.
What Bernie is promising is not possible in the system. It's pie in the sky things, that sound great on the campaign trail that will never the see the light of day. Not for the sake of him pushing it, but a republican controlled house will NEVER allow any of his policies to be implemented. Free tuition? Will never happen, never even pass the first draft in either congress or senate. The lobbyist will kill any mention of that. The president can't write laws. Obama spent 8 years fighting congress to pass anything worthwhile. In the end, he passed a health care bill that was diluted, and something everyone hated. He was for change. Remember that? He couldn't deliver, because in the end, he was just fighting the other side.
Ending corruption? How he is going to do this? Take money out of politics? Same thing, will never happen. Will never even be brought up for debate. Fighting Wall st? Same thing; how is going to do this, when the other side will never allow it to happen. Most democratic senators and congressman take money from wall st, they'll shoot it down as well. What change is he bringing? In the end, most americans see Bernie that is not only unelectable, but too much of a idealist/purist to ever get anything done even if he was elected.