Lost of labor hours are the real answer.

Basically what would happen was that someone would write it down on a paper form, mail that form off to the typing pool at the corporate headquarter where some clerk would then type it into the central system with a delay of 5-10 days from point of sale to recording into the inventory management system being totally normal, leading to a lot of overstocking and waste.

So to run offline would mean getting a hold of a lot of people that aren't there anymore in addition to reintroducing all of the risk(and fraud opportunities) that running without real time access to centralized data.