I always heard they were a casualty of the Gun Control Act of 1968. That changed the way Americans could buy guns and it now required a dealer to recieve them. Have read that in several places. Maybe it is true, maybe not, just the only reason I ever heard.
They were before my time, but I do get a kick out of reading the old catalogs. Everything they had was made under a suoer secret patent, made of kryptonite, defied laws of physics, and all kind of things along those lines. Fertile minds in their advertising department, that's for sure!!!