When UK Labour exited government in 2010 a note was left in the treasury office to this effect. It was tongue in cheek but nevertheless reflected Labour Party thinking. It was seized upon by the Conservatives who have mercilessly whipped Labour with it ever since.
Instead of turning this on its head the party sought to correct it by parroting the austerity message. When the reins of the party’s leadership were taken over by the left, a counter narrative was presented and got popular support. However the press and entire establishment declared war and crushed the movement.
The US and UK political systems don’t tolerate this dissent. The Democratic Party, after decades of pushing this narrative, is now enslaved by it and is in self preservation mode. This is no excuse but goes some way to explaining what is going on.