As I recall the switch (to the lighter bullet) was based upon (1) weight factors (2) a wounded soldier requires 2 more soldiers to carry him off the field so that it actually temporarily takes three people out of service (3)less recoil and muzzle rise for those less experienced marksmen.
Also add that there was a philosophy going around of putting more lead out as opposed to training marksmen. This turned out to be a bad idea - "spray and pray" has never worked very well.
That was the reasoning, and the caliber worked very well for the intended mission. Unfortunately, we don’t get to use fire and manuever against insurgents.
IMO, the biggest problem is not the rifle, it’s the way it is used. My father described WW II urbam combat tactics simply.
Throw grenades into the building. Bust the door. Machine gun everything. Secure the building and move on. If you don’t want to go in the building, get tanks or guns to destroy it.
Now we prosecute soldiers because they did this during a firefight. If we’re going to send men to fight wars, we must let our guys win.