They cared once upon a time. The watershed may have been with the civil rights movement. At that time, liberalism may have shifted focus from the economically disadvantaged to the structurally disadvantaged - disadvantaged by race, and then by gender, then by sexual orientation, then by not being sexually binary.

In doing so, though, those who were economically disadvantaged felt that the liberals - at least as represented by the Democrats - didn't care about them and their problems. This was a major factor in Trump's election.