I have no idea. You'd have to watch the video as Orrin Hatch reads the whole article that Williams wrote. And Hatch clearly said that although Williams is not of the same political beliefs, that at least he gets it. Hatch back then said Williams was a "great journalist." In the Pirro - Williams video, Williams is bad-mouthing Hatch because he said Ramirez's allegations were phony. I doubt Senator Hatch would call Juan Williams a "great journalist" today.
I found this from Vanity Fair in 2012:
In 1980, he began writing for the Post editorial page. That December, at a convention for black conservatives in San Francisco, he met 32-year-old Clarence Thomas, then an assistant to Senator John Danforth of Missouri. An op-ed column Williams wrote praising Thomas—whose conservatism was, Williams wrote, “born of the same personal anger at racism that fired the militants of the 1960s”—called him to the attention of the Reagan administration, which led to his first presidential appointment, which effectively led to the Supreme Court. (In 1987, by which point Thomas headed the Equal Employment Opportunity Commission, Williams profiled him in The Atlantic. The notoriously wary, reclusive Thomas opened up to him: what resulted was by far the most probing and insightful piece about him ever written. Williams and Thomas have remained friends and still lunch together occasionally; Thomas attended Williams’s 50th-birthday party.)
Most likely because Justice Thomas is a black man and Juan did not like what was being done to him. Took it more personal than Judge Kavanaugh today.