Except that now even Sanders accepts that he has almost no chance of winning.
You may not remember, but Clinton lost the primary in 2008. She led it for a while though. And while she did there were the same accusations of dirty tricks and a system rigged to elect her. But then Obama captured the lead and won. EVERY primary, hell every election, has allegations wrong-doing and of shutting out voters. But all the time they are simply proven to be sloppiness in the voting process; nothing is perfect, especially things run by the government, doubly so when volunteers mostly run them. Voting is like going to the DMV, there are rules, lines, and it’s rarely a pleasant experience.
If Bernie were as popular as you say, he’d be winning. But minorities and the poor are skeptical of him. Polls are interesting, but the only results that really matter are election results.