Bernie is a good counter-example. Huge rallies, way behind in votes.
You can find signs that people in the establishment personally favored the establishment candidate – the least surprising revelation in political history – but there's no evidence that lead to any concrete action. That's why the only claims of rigging have been intentional misrepresentation based on the knowledge that some people like you would repeat those claims without checking the sources.
Hint: it's the same reason why the alleged victim is going around telling his supporters to vote for Hillary. If you trusted his judgement enough to think he should be president, why not trust his analysis now?
And that reason is elementary game theory. The only people with incentives to claim that the Democratic primaries were rigged are those who will be left with no political influence if the Democrats fare poorly.
When the Republicans do well, it's because they value party unity over literally everything else. One of HRC's strengths is that she brings the same thinking to the Democrats. For anyone within the party, working against her carries no conceivable upside. And as we've seen in DWS's case, working for HRC means you'll be well taken care of, no matter what.
Basically, if Sanders or anyone else on the left has beef with the DNC, they will be much better off if they wait to bring it up until after the election. And maybe not even then.