We're getting 4 years of gridlock minimum so I'm guessing this is over the possibility that the margins in the House are now slim enough for the squad to block the oncoming austerity measures. They wouldn't be able to stop it entirely, but it would force the democrats to cross the aisle and pass those bills with republican votes, while having to spin the bill against the most popular members of their own party. Mitch also has a lot of incentive to either block or demand concessions since red states already cut social services so badly that South Carolina is actually coming out of Covid with a budget surplus.
Nobody really knows how safe the safe seats actually are with that bullshit polling and heads are certainly going to roll in the midterms. So at that point the only option is to try and say it's the craaaazy lefties who killed the recovery and if we just got rid of them we could really get things done.
My theory is after Bernie's run and Occupy we went into overdrive with anti-socialist propaganda. Except in America what constitutes socialism is so broad that what results is really just anti-collectivism. Instead of only eroding the cohesion of anti-capitalist groups, it harms the ability of any group to form a collective effort even if that effort is pro-capitalist. For some people categories like black, white, latino, or LGBT then become thought of more as forms of self expression rather than groups of people who have any special responsibility to each other.