Whether or not the thing keeps soldiers alive is actually pretty far down the list of reasons to control the supply chain (see, for instance, the various review

Whether or not the thing keeps soldiers alive is actually pretty far down the list of reasons to control the supply chain (see, for instance, the various reviews of the M249, or the specific small-p political decisions around the M16 design. I've heard first hand accounts of Afghan National Army/Police answering calls while the US Army operated cell phone jammers a few feet away). The main thing is consistency. If you can depend on depend on your machine gun to jam if you fire it for more than 3 seconds, then you just don't fire it for that long. But if you have no way of knowing how many rounds you'll get out of it (if any) before it jams, you'll just stop using the thing. Further, a lot of the procurement rules devolve down to "is this supply chain a strategic weak point?" We don't buy our HMMWV tires from Russia not out of quality concerns, but to deny them that weapon. So the testing is done to verify provenance, rather than quality.