Maybe the brass is looking at future conflicts on the table?
America has stopped producing Riflemen, so the volume of fire doctrine was adopted to allow the few real killers to do the work while everyone else stayed busy (On Killing - Grossman). That's why we needed more carry capacity.
Now, the push for 7.62x51 performance out of a CQB rifle seems to be the goal. A 13" barreled rifle producing those numbers needs the 80K pressure this round has. Not sure how that will play out for longevity of the platform, but somebody will be making $$ as we switch over and maintain this new platform.
Interestingly enough, the 6.5 was right there in performance.The Brass was not willing to change the grooming standards so everyone could switch to the required 'man-bun' hair styles for its use. Although, it was a quite effective interrogation technique to repeatedly tell the enemy combatants, "I shoot a six-and-a half".
