This article does a great job of explaining people's frustration with having to vote for Biden again. It's long, so here are some quotes. They're totally cherry-picked, I'd recommend reading the whole thing (especially if you think the problem started with Biden, and that Clinton and Obama were ever good choices).
during the 1980s and early 1990s, fears of a relentless Republican juggernaut pressured those left of center to take a defensive stance, focusing on the immediate goal of electing Democrats to stem or slow the rightward tide.
Today, the labor movement has been largely subdued, and social activists have made their peace with neoliberalism and adjusted their horizons accordingly. Within the women’s movement, goals have shifted from practical objectives such as comparable worth and universal child care in the 1980s to celebrating appointments of individual women to public office and challenging the corporate glass ceiling.
Each election now becomes a moment of life-or-death urgency that precludes dissent or even reflection. For liberals, there is only one option in an election year, and that is to elect, at whatever cost, whichever Democrat is running. This modus operandi has tethered what remains of the left to a Democratic Party that has long since renounced its commitment to any sort of redistributive vision and imposes a willed amnesia on political debate.
I mean, you probably should vote Biden this time, because he's not all that bad, he's done some good things. And trump is so terrible, it probably will be the end of democracy and the victory of fascism if he wins. Right? But what about in two years time, or four years, or eight years?
Absolutely, primaries are for exactly that, the actual November election is about damage control.