Title. Similar to how sidearms work in Left 4 Dead, having infinite ammo for primary weapons allows them to consistently be reliable. Perks like Drop Mag burn through ammo so quickly and force you to wait just so you can Regenerate it.
Removing primary ammo from the game makes them so much more consistent, and allows a good backup after your special is dry. Plus, nobody should be unable to stun a champ because they’re out of ammo.