That's because "the left" actually believes in the enlightenment narrative of facts and consistency.

The enlightenment project was always an affair of the  middle class. It was most influential at those times when this class composed the majority of the electorate. As the franchise was extended to those lower down the ladder the enlightenment narrative became less compelling. In the USA Freemasons served to convey many of these values to emerging members of the middle class.  However the majority of the population retained allegiance to "that old time religion." One of the reasons emerging members of the middle class found enlightenment values so attractive was that gave them a perspective on religion that enabled them to develop a relatively integrated, rational faculty, which is useful in business and public affairs--until the adherents of "that old time religion" figure it out and react.

It was elites who proclaimed in the famous 1960s issue of Time Magazine that "God Is Dead."  The right seized on this and rode the backlash into dominance in the 1980s.  What left there remains in the USA has been swimming against this "dark ages" undertow every since.

"It is not necessary to have hope in order to persevere."