They are losing money on the $15 fitting fee. There is some margin built into the price of the barrel, of course, but they cannot take an action in the door, put it into the books, track it through the process, get it out of the books, label and package for shipping for $15.
At the same time, they can't tighten specs enough to make the barrels fully interchangeable because of all the shotgun and older actions out there. They are caught between a rock and a hard place.
At some point in the future, they will likely make a slight model change so that new barrels will no longer fit older or shotgun actions and can be made fully interchangeable among new actions. A slight change in the hinge pin diameter would do it. My crystal ball ain't clear enough to tell me when that will happen.