Their message for the last ten years (plus or minus some) has been that if you think that an unborn baby deserves legal protection, if you don't think that trans people belong in womens' restrooms and on womens' sports teams, if you don't think that gay marriage is a good idea, then you are an irredeemable moral leper, and their goal is a complete destruction of your culture. If you're, say, poor and white and blue-collar, they still are totally against you, even though you're the people that they have, historically, represented.
A bunch of those people voted for Trump (or didn't vote at all), knowing what Trump was. They voted for the guy who at least pretended to care about them.
And, really, why did they expect a different outcome?
That's what the Democratic Party has to do with the current US government. Them abandoning their core constituency is a critical enabling step for us to be where we are.
Does that make it all their fault? No. But wow, did they ever bungle both the 2016 and 2024 campaigns.