If you graph the electric field strength along a photon’s flight path, there are points where it is zero. Same for the magnetic field strength.

The energy of the photon is transformed continuously between electric and magnetic field potential, and if you consider either of those signals the energy is coming into and going out of that medium repeatedly.

Because each of those non-zero periods of field potential happens in a particular spot in space (those fields don’t move; they grow and fade in sequence), I’m saying that region of space has absorbed the photon.

Of course, you know, particle wave duality. So in some ways they travel smoothly as well.