The AR platform is no longer lethal enough for the Military.

[yagotme]

24. Google, much?

https://en.wikipedia.org/wiki/M16_rifle#:~:text=The%20original%20M16%20rifle%20was%20a%205.56%C3%9745mm%20automatic,to%20become%20the%20US%20military%27s%20standard%20service%20rifle.

In 1958, the Army's Combat Developments Experimentation Command ran experiments with small squads in combat situations using the M14, AR-15, and another rifle designed by Winchester. The resulting study recommended adopting a lightweight rifle like the AR-15. In response, the Army declared that all rifles and machine guns should use the same ammunition, and ordered full production of the M14.[23] However, advocates for the AR-15 gained the attention of Air Force Chief of Staff General Curtis LeMay. After testing the AR-15 with the ammunition manufactured by Remington that Armalite and Colt recommended, the Air Force declared that the AR-15 was its 'standard model' and ordered 8,500 rifles and 8.5 million rounds.

Yes, the M-14 was difficult to control in full auto. Yes, it was heavy, and the ammo was heavy. Above excerpt proves my point, though.