The government is getting sticker shock on the price of the new ammo since there's no civilian market to offset it and none of our allies field that weapon.
This is an interesting take, and not outside the realm of possibility.
This end of 5.56 sales to the civilian market is a business decision based on scarcity of resources. The government only has this plant running to make their ammo and there are only so many Machines that make rifle rounds. I think this change to stop selling to the open market is the need make the 6.8mm round. There are only so many machines to make rifle ammunition and to ramp up the new ammo they need some of the equipment that made 5.56 and they need the rest to still make 5.56 for the rest of the military not getting the new rifle and machine gun.
You have to remember that the plant is support the military not the civil market. They sold to the civil market as they filled their need , yearly use and war stock rotation, and to keep the workers and the company operational so there was not stoppage of production and layoff of employees till the next run.
In one sense this is good political timing to make anti-gun people think the administration is doing something about feeding the AR by limiting ammo. But I think it was bad messaging without an explanation why the policy change that is now red meat for 2A community that the government is against them.