They started to appear in the 1950s, when roller bearings became common on new cars. Since most of them were applied to existing cars, they tended to last until the car itself "aged out". I know they were still quite common in the late 1970s, but didn't see too many trains after that, as I neither lived nor worked next to a railroad after moving to Kentucky.
The conversion itself was simple, not much harder than changing the bearing brasses on solid-bearing trucks, so a lot of railroads did it as a cheap upgrade. It didn't make the car any better at hauling stuff, but virtually eliminated the danger of hotboxes, and reduced rolling friction, saving fuel.
