See: FAL vs. M14.
Also see: Magazine PiP.
Magpul's followers have been out for a while and work fine...but the military wanted their OWN follower...
The military is infamous for spending millions developing "their own thing" when superior civilian products exist and continue to be used instead of whatever crap they dream up on their own.
That was the most recent public example of 6.8 mm in military/government use. There have been other less publicized deployments. Note that MURG conclusively demonstrated 6.8 mm combat system capability back in 2006.
Also keep in mind that 6.8 mm was intended as an interim and expedient upgrade to existing M4's to allow them to quickly be modified to over-match our opponents 7.62x39 mm systems back in 2001-2002. These days there are better choices available for a combat cartridge, for example AMU's new .264 USA, Cris Murray's optimized 7x46 mm, or even a cased telescoping 7 mm...
For civilian and LE use, 6.8 mm is an easy way to provide substantially better terminal performance in the AR15 FOW over the typical engagement range of a carbine.
Facts matter...Feelings Can Lie
Don't you go changin', crazy internets!