Further to Genghis' reply -
the reason for not using WT data is that the thing the pilot must refer to for all flying, the airspeed indicator, is not going to be indicating completely accurately - wind tunnel data would use absolutely accurate airspeed.
So, even if the wind tunnel data were completely valid, it would be necessary to find a way to translate that to the real aircraft, with the real pitot static system, and no-one has found a way to do that.