There is a reddit comment that I condensed that summed it up well.
Blue MAGA is a term used by progressives and leftists to define liberals who tends to punch left with “vote blue no matter who” rhetoric, especially when dismissing criticism of the Democratic party and candidates, who generally conform to all the negative neoliberal stereotypes while demanding that they still get support because the other guys are worse.
Obviously, those people and others feel the same about “Genocide Joe” and that the lables still apply in the current election, where the same discourse from liberals is happening again.