It's probably a mix of things like an oiling problem or something that causes the lifters to not move up and down in their bores as easily as they should and weak bearings in them that can't take the added force when that happens. There's very little friction between roller lifters and cam and it seems that this has only become more of a problem with newer engines. Don't forget GM v8s also have the same sort of problems and also started around the same time.

Even with older roller cam engines you can open one up that had engine failure from oil starvation and the cam and lifters look perfectly fine.

There are also posts kicking around other forums, usually by the same small number of people it seems, that blame the failures on lack of friction because of certain oils which cause the roller to not roll on the cam.