An answer I found online was: At high altitude where molecules are far apart, scattered photons can travel without interfering with each other, thus they fill the sky with blue light. But at low altitude, molecules are so close to each other that scattered photons destructively interfere with each other to cancel each other out, that's why we see air as transparent. However, if they perfectly cancel out, then wouldn't the energy be not conserved?
Another explanation was simply that the effect is only apparent in a very large column of air since the scattering effect is not that noticeable.
So why doesn't Rayleigh scattering happen at low altitude in air?