Let's call them what they are:

[benEzra]

74. Because they were spec'ing it for use in automatic weapons.

They traded off per-round lethality to get usable select-fire capability, which was and is considered vital in CQB by the military; 3-round burst on the M4 is now acknowledged as a Fulda-Gap aberration that is now being rectified (the M4A1 is back to full auto, based on experience in Iraq and Afghanistan).

To my knowledge, the U.S. military, and all other militaries on this planet, have not procured a single .223/5.56mm semiauto for general issue, ever; all military semiautos ever issued were at least 7mm that I'm aware of (the Garand was originally prototyped as a 7x51mm). I believe some private security contractors have occasionally used a few 5.56mm DMR's as gap-filler precision rifles, and it's possible some of those have occasionally seen use with SOCOM for weight reasons as well, but nothing for general issue and especially CQB.

Would you prefer that all our rifles were rechambered in 6.8mm SPC, which was developed by/for SOCOM to offset the .223's lack of power? Or perhaps that we all switched to AR-10's in .243 Winchester? A 58gr varmint bullet at 3,925 ft/sec would be a pretty effective defensive round, would it not?