It mostly just seems that way because social norms shift over time, mostly (thank goodness) to embrace progressive ideals.
In the 19th Century United States a “conservative” might be someone who supported the institution of slavery and a “liberal” might be someone who thought non-white people should be free to lead their own lives—but preferably somewhere else. Believing that a black man or even (gasp!) a black woman might be capable of running for political office and governing white men wouldn’t just be “liberal,” it would be downright RADICAL.
Just a few years ago only “liberals” openly supported gay marriage. Now centrists and even many conservatives do too. There are plenty of people who have held the same political views for most of their lives who were once considered “liberal” but would now be considered “conservative.” That’s how social progress works.
