Planes only use GPS because GPS has a very rigorous signal integrity program that others don't have. The "safety of life" requirements on GPS are onerous. Also, GPS has both L1 C/A and L5 (not enough L1C or L2C to be useful yet) signals. I don't think Galileo or GLONASS have extra signals, but I think Beidou does (not an expert on other systems).
Just this January, ESA completed the safety of life analysis requirements for Galileo to be used as a civil aviation signal.