Cheap construction, off-shore suppliers, cut-throat pricing, hecho en mexico, inferior metals. Some, all, or most of the above.

Years ago, I never had a cam fail. I did some rather radical (for the street, at least) cams from 6-cyl Chevys to Pontiacs, to SB & BB Chevys. Granted, I didn't do dozens, but I never had one take a dump.

Now, I wouldn't put in anything but a full roller.