Exactly.
While part of the model is to develop players we can sell on, that won't (and can't) be the case for every player we develop or sign. First and foremost we need players that will perform in the first team every week. Professional football is supposed to provide entertainment, not shopping.
If we sign a player for free and they contribute for a couple of years before moving on, then that was value for money. Same as when any of the rest of us change jobs without our ex employer receving a transfer fee.