This is the naive take. Been voting since '08, almost exclusively Democrat. The centrist/corporatist democrats who dominate the party really get off on running against fascists, because it’s like being in a political fast food diet. You don’t have to really prepare or deliver complex policy goals, you don’t have to piss off your corporate donors, you just stand next to the fascists and say “we’re not them; you don’t want fascists running the country, do you?!” Problem being that fear only gets you so far before people stop responding to it, the fascists win an election, people get scared again, and the democrats get another big shot of engagement and fundraising basically for free.
The centrist democrats don’t want to move left and frequently work to shut down actual left politicians in and outside the party. They don’t want to stop fascism because then they have to actually work and compete instead of let fear do the work for them