Because redoing the primary is an absurd idea

And I am, probably to an excessive and embittered degree, made cynical by the amount of open propaganda in and out of the media which is attempting to put out bad ideas on purpose to hurt the Democrats and help the fascists

And you’re not wrong. A contested convention would be a massive shit show which might doom the Democrats in the election irrevocably. But it might also produce a nominee with some kind of mandate, which would be nice. It would also be feasible to do, whereas holding another primary election would not.