I think the problem is that most people think nothing ever happens, or to put it bluntly "It couldn't happen here". Harris literally offered nothing - when pressed she even said that she wouldn't have done anything different from Biden, which is the last thing you want to hear about a president whose only selling point was not being Trump and giving the country breathing room to come up with something better. Yes, the US recovered faster and stronger from COVID and the recession than the rest of the world but that doesn't change people's lived realities of living paycheck to paycheck with prices only ever going higher.

People don't "learn their lesson". Accelerationism always fails. Suffering, fear and looming threats are what enable the rise of authoritarianism and autocracy, not what helps overcome them. Fascism is rarely overthrown by a popular revolt that establishes direct democracy and egalitarianism. It's usually overthrown by a military junta or gradually coalesces into an oligarchy that reintroduces the trappings of liberal democracy to placate the masses.

As much as the American right loves to call the Democrats "radical leftists" or "socialists", the Democrats have nothing to offer in response to the people's suffering. The Republicans can at least lie through populism: claiming to be opposed to "the swamp" while installing their own loyalists and family members in positions of government, claiming to fight the "coastal elites" while implementing the whims of billionaires, claiming to defend "freedom of speech" while prohibiting government agencies from using progressive terminology, etc etc. But the Democrats can't even do this because at best they can offer half-measures or compromises. They couldn't even pass the Green New Deal and now the Trump government keeps referring to it as if it had actually been implemented.

This isn't a uniquely American problem. The social democrats in Germany have recently come out in opposition to voting on initiating the process to investigate the far-right AfD party (which Elon Musk has been actively supporting btw, which is an unprecedent level of foreign influence) for qualifying for a trial to be banned as unconstitutional (i.e. roughly equivalent to proposing a grand jury with the outcome being a constitutional court trial being launched or not). Why? Because if they would participate in such a vote and support it, "all democratic parties" should support it but there's a good chance the conservative party would vote against or abstain and this would "hurt the democratic parties" by making them no longer unified in their opposition to the AfD - or that if the conservatives were to vote in favor, this might radicalise some of its supporters to vote for the AfD instead. Mind you, the conservative party has already repeatedly cooperated with the AfD and they have supported each others' proposals, although the conservative party is officially ruling out any potential coalition with them while incrementally adopting their rhetoric. The socdems are too concerned with protecting the optics of the system itself and maintaining decorum to directly attack a party that is fundamentally opposed to the principles underlying that system.