Hmmmm.

OK. Consider this.
The OEM system has a known intake pipe diameter, and the MAF sensor is located in a known position within that pipe. Therefore, with some logic, it can calculate the lb/min of air traveling through the pipe. The PCM monitors the air intake volume and temp, MAP, engine load, fuel temp, TP, among others. The PCM calculates what each value should be under given circumstances. If you change one parameter, the PCM will expect to see corresponding changes in others. If any of these parameters are outside of what the PCM considers normal, it will try to correct the perceived problem. One of the first things it will do is defuel. If you operate outside of the PCM's envelope, it will defuel. An increase in air volume alone, without the presence of a corresponding fuel, MAP, or engine load change will be perceived as a problem the PCM will address. Fuel is not metered according to air intake volume alone.