You say "better options" but a clear majority of Democrats thought Biden was the better option. And all the other candidates that anyone took seriously are in the same age range as them. Nobody younger knocked on the door with a platform really worth backing. Buttigieg had no Federal chops whatsoever, Harris was a freaking prosecutor.
Or if you're just talking "better in general", then you're talking about the Progressives war. Bernie still hasn't realized he'll never win a Primary, and the way his campaign sabotaged and undercut Warren's with necessary voting demographics was a killshot. Grassroot movements to call her a secret Republican. They should be ashamed of themselves.