Because they are made from a poor grade of metal, hence the failure. It wouldn't matter if you had all the oil in the world, the FACTORY cam will fail. Its NOT a oiling issue
370 Hemi on ChargerForums.com has had the hardness of the camshaft and lifters assayed by Stephen Walsh, who appears to be an engine lubrication expert, and who informed 370 Hemi that the metallurgy of the cam and lifters was just fine:
