The DNC does that, not the presence of a Democrat in office. They campaign so hard against any actual progressive candidates and push their own chosen one even to the point of losing elections. What does it tell the American people when the DNC would rather have Trump in office than Bernie Sanders?

The superdelegates paint a false picture leading into the primaries and the news outlets spread that on repeat. For some reason the majority of Americans don't seem to understand how super delegates work, and assume the races are already over before they even start. Then everyone gets defeated and loses faith in the system.

But your second proposition also holds true. Trump, Desantis, Cruz, and all those types of candidates are exhausting. They're supposed to be exhausting. They're supposed to throw so much fuel on all the fires that everyone loses track of which ones are burning hotest and then eventually just gives up. The strategy works well for them.