The reason for using nitrogen in aircraft tires has to do with high pressure. Except for light aircraft (think Cessna, Piper, etc.), aircraft tires operate at very high pressures—hundreds of psi. It’s much more practical to use a high pressure gas cylinder/regulator to fill them than an air pump, and if you’re gonna choose a gas that is readily available in high pressure cylinders, cheap and relatively inert, nitrogen is the most practical choice. The kinetic diameters of N2 and O2 are so close that there’s no appreciable difference in permeability through rubber, but pure O2 would probably break down rubber faster due to it’s much higher chemical reactivity.