The availability of NC/NF is only a clue to whether an SWU can be confirmed at time of purchase, right?

It seems so obvious that one would want to know if they are going to be certain about the upgrade before plunking down extra $$$ for W rather than a cheaper fare bucket, or even purchasing a fairly expensive international ticket. UA can't program the .bomb to do this, or it has some reason for not doing it? Hard for me to imagine a reason for not doing it, since it only means a 1K taking up more time on the phone looking for flights that will confirm at time of purchase, or that they can't program the .bomb to give this information. But then we are talking UA and its often eccentric .bomb, aren't we?