Because you're relying on the quality of the mic, plus the ability to capture the readings in what is often, but not always, a USB interface at worst, or a small pro-audio ADC at best. Because of the above factors, not failing to mention the variable quality of the software in use, I've seen readings taken in the exact same spot of the room have differing curves from one reading to the next.
Therefore, as audio is a game of inches, where most of us try to squeeze the last bit of sound out of our gear, within our means, this variance can be too much when dealing with small frequencies and time.
I believe it took a radically different approach to room correction in order to allow the adjustments in the environmental domain as opposed to the theoretical, captured by like software, yet with too many variables to be as precise.
Therefore, as audio is a game of inches, where most of us try to squeeze the last bit of sound out of our gear, within our means, this variance can be too much when dealing with small frequencies and time.
I believe it took a radically different approach to room correction in order to allow the adjustments in the environmental domain as opposed to the theoretical, captured by like software, yet with too many variables to be as precise.