Simple (not really): Every time a photon passes through a medium, like say - glass - that photon gets distorted, at least to some extent. You must now correct for that distortion and you do so by... wait for it... passing it through another medium.
Uh oh. You've distorted it in an entirely new and exciting way. Which must now be corrected for. Guess how that's done?
So photons just started doing this in recent years?
So photons just started doing this in recent years?