...And,I can tell you why: The employees who worked in the Bay City plant where these and the 305 V-8 cams were cast were told to rush them through the heat-treat process to keep up the production numbers. I worked with a number of those folks when I worked at the Saginaw Foundry,where many of them had transferred to. They were threatened with termination after reporting to their bosses that the cams were not being completely treated and were told to just "keep the line running-or else". Doubt what I say? I spent 35 years in various GM plants and have a hell of a lot of similar stories.
Now;the worst mill I ever dealt with was the GM 3.4 liter Dual Over-Head Cam V-6 from the late 1980's/early 1990's. Myself and the other Test Mechanics in the Lab referred to it as the Dork or Joke engine. It used "spiral" springs on the ends of the cams,which naturally came loose(usually at 6000rpm on the dyno) and were an absolute bee-otch to work on. While the V-6(3.8L/90 degree) Buick Gen 1 and Gen 2 were tough as nails(I know;we beat the shite out of them on the dynos),perhaps the toughest was a little 60 degree 3.1 liter V-6 that we ran for a while. Totally gutless,but would we could wing it to 7grr+ on the stand and it stayed together. At the request of an engineer,we actually tried to break one by trying to take it to 9 grand-the absolute limit of our dynos. We broke the dyno,not the engine. Tough little SOB,that one.
I've known mech's at a couple of foreign-car dealers who swore at the various designs from Asia-mostly due to the complexity of the mills. Hard to beat good ol' pushrod simplicity.