The frame and locking block cracks were effectively operator induced. The bulk of the cracked frames being reported came from the SpecWar community who, after much arm twisting and dodging the question, admitted that they had been using basically +p+ ammo that the weapon wasn't designed for. The locking blocks were caused by over zealous armorers grabbing a new one and installing it without properly checking the gaps between the lugs and frame. If they are not nearly identical the block torques and shears off, requiring ANOTHER block. That's why for a long time Beretta had a mandate that any barrel or locking block replacement required the entire pistol be send back to the factory for the work to be completed.
Not 'zactly...
Too many early M9s cracked frames, blocks , and slides at low round counts having fired nothing but approved mil-spec US M882 ammo (which generates pressures above the SAAMI +P limit BTW). In the late 80s 12 Berettas were tested to slide failure w good M882 ammo and all 12 broke w round counts from just under 5K to just over 30K. By the late 90s M9 slides tested to failure were averaging 75K w a range from 55K - 95K. Somebody fixed sumthin' that wasn't broke: the guns, the ammo, or the testing?
M9s at the local base rarely break anything under 22K, and the most likely thing to go then is the block. Replaced blocks do not last as long if they are not fitted, and most are not fitted they are just dropped in. The contract specified parts would not require fitting and they don't. You can drop them in, so they do; they just don't last as long if you do fit them. The M9s would do better if recoil springs were changed every 5K rounds, but there is no requirement for that, so they don't unless a pistol comes in for something else.. Even so, many training M9s at the local base have over 50K through them, much of it w the Win +P+ frangible ammo.
BTW, the only part w a specified service life in the original M9 contract was the slide, and it was for just 5K rounds. IIRC, the specs for the next service pistol have a min service life of 25K.
The military has conducted numerous market surveys and limted field trials over the last few years to see what is available, what the troops like, and how what they like fits w what the military wants. What's best for a highly trained operator w big hands is rarely best for troops w small hands who shoot once a year... why you see things in the specs like a manual safety and adjustable grips, etc.