Because you can buy cheap 223 by the case in bulk, reloading for plinking ammo doesn't save you the same sort of money that reloading for other calibers can.
Pistols can be cheap to reload because of the tiny amount of powder used, and the ability to use cast lead bullets which cost very little compared to jacketed projectiles.
Rifles can be cheap to reload because you can make high-quality ammo for the same price as buying cheap ammo from the store.
The big advantage to reloading 223 is that you get a much better quality product, compared to the bulk ammo. If you are only shooting at 50 yards or less, this might not really matter though. On the other hand if you shoot at stuff thats more like 100-200+ yards, then higher quality ammo is a good thing to have.
The other thing to consider is reloading rifle ammo with a single stage press is pretty easy to get into, but if you are the kind of person who blows through 500 rounds in a single day, then you'll be wanting something faster and prices go up fast when you wanna get reloading done quickly AND accurately.