There are some subtleties, like slight turns of the body or the wrist on certain pitches, or not rising up too high to catch a pitch near the letters. But for the most part it's just difficult to actually do it at a top level while also worrying about so many other things. There always were guys who had the reputation as being good receivers. What's new is the attempt to actually quantify the advantage (or disadvantage, depending on the catcher.)