What went wrong with these cam bearings?

First guess, not enough clearance. Second guess, crap in the oil passages. Third guess, no prelube or damaged them while installing the cam. In that order.
ALWAYS check to see if the passages are free and clear and that the holes in the bearings line up with those in the block. Prelube the bearings (I use Lubriplate 630AA or cam lube) and prelube the engine via the oil pump shaft prior to start up. This is critical.Just before you start it for the first time, pull the plugs and coil wire and crank it through until you have good oil pressure indicated. This will prime the pump prior to start-up. The first 3 minutes of a cam's life are the most important!