Because the candidate doesn't matter anymore. You will get some shit propaganda narrative hammered into your brain anyway (see: "vote for Trump so there will be no genocidal war in the middle east").

So why would democrats care about anything else than their own internal power dynamics? It's not like they can get a good candidate when collective brain-damage will make sure that it's a totally useless candidate anyway once the screeching morons on (social) media tell you what your new reality is.