Excellent question.
I have never registered as a Democrat, nor have I ever voted in a Democrat primary (makes no sense because I live in a pretty red area and usually the democrat primaries are uncontested). But my wife and her family are mostly lifelong Democrats.
That said, I think the opposite is true, and that most Democrats felt like Biden was "forced down their throats" and longed for another choice.
They all knew Biden was old and questioned whether he should run again, and many were disappointed that the Democrat party seemed to shut down any other challengers. And face it, unless you are a complete idiot, you knew a vote for Biden had a good chance of being a vote for Harris anyway, because at 80+ years old, the chance of Biden not finishing another 4 years was high. I also think most Democrats know that had Biden made the decision last year, the chance that Harris would have won the nomination anyway is pretty high.
Also consider that it is only relatively recently in US history that party voters had the opportunity to choose their party's candidate. Prior to that, it was party delegates, and who those delegates voted for at the convention was only minimally influenced by voter input. Parties set their own rules. Do libertarians have a primary? Green Party? "We the people" party? Reform party?
Having a major candidate drop out so late is new; but a party choosing a candidate without a primary is not. The party sets their rules, and from the looks of it the vast majority of Democrats seem quite okay with how things worked out. The only ones complaining are Republicans, basically making excuses for the fact they are now behind in the polls.
