You seem to be under the mistaken impression that Capitalism is about "How much can I spend?", and not, "How much do I own (and how can I leverage it)?". Property like media outlets, where you can do things like manufacture consent (e.g., convincing black voters that the man who railroaded Anita Hill, and who called the most virulent segregationist of his generation a dear friend, cared about black folks' interests). Like your party's national committee, where you threaten members and candidates with persona non grata-status for campaigning or endorsing against your whims. Like the
candidate himself, who initially did not want to run in the first place.
All of these things represent influence - influence that, like other methods used to induce fear and panic, can undermine both individual's rational decision-making process and their capacity to express their raw feelings.
Let's be clear: there was zero broad enthusiasm for Biden's policies (partly because he refused to detail them). But leveraging influence can allow you to take an electorate that, by all measures, wanted Bernie Sanders' platform - with M4A and the GND in particular being wildly popular - and turn it into one that checks the box next to Biden's name instead. What you get is not an expression of the electorate's will or desire, but of their terror.
So, actually, the influence of Capitalism (through the means I spoke of earlier - in a word, corruption) readily explains Biden's win in 2020. He was not a good candidate, he was not a good president, and people did not want to vote for him, but felt forced to, because an overwhelming amount of capital was leveraged to that end. People, in fact, did choose Bernie, until coerced not to. And that was simply a matter of people with wealth getting what they wanted. It may very well be that you only get to stand up to that force once in a lifetime, and Millennials had already elected Obama.