[doubleunplussed]

Well, black-body radiation is still peaked around a certain range of wavelengths depending on the temperature, it's not just equal power at all wavelengths.

Light visible to humans is at the peakiest bit of the sun's black body spectrum, see here image here: https://i.sstatic.net/kRUju.png

Green isn't just the wavelength the atmosphere lets through the best, or the wavelength humans are most sensitive to, it's also the peak of the sun's black body spectrum.