Why is wireless avionics intra-communications (WAIC) not used for air-air or air-ground communication?
WAIC is designed to be extremely low power.

Its low power is not be enough to reliably reach a receiver on the ground, satellite, or other aircraft.  Increasing the power would create all sorts of other problems, including problems with spectrum allocation, and data collisions.

There is simply no demand for a more complex system to do these other tasks.

The basic engineering principle is KISS