You failed to "run in" the cam at RPM well above idle for 20-30 minutes immediately after startup. While a cam is establishing a running fit with the lifters, it's vitally important to keep it flooded with lots of oil thrown off the crankshaft by running at 1500-2000 RPM, and bringing the speed up as soon as you see oil pressure on the gauge. Most cam manufacturers also provide a tube of "assembly lube" to be applied liberally to the cam and lifters on the initial assembly. This protecrs the parts until a good volume of oil can be supplied to the lobes by the spinning crankshaft.
Some "break-in" oils contain a high concentration of an additive known as "ZDDP" that's a zinc compound intended to assist a flat-tappet cam break in properly. Most modern oils have little or no such additives because modern roller-tappet cams aren't as sensitive to catastrophic failure during the run-in period.
As an aside- - - -all that cam lobe material had to go somewhere- - - -do a complete teardown on the engine and pressure-wash all the crud out of the oil system or the next failure will be most of the rod and main bearings, etc.
Jerry
