Think of a photon as a wave form with a frequency - just like a radio wave. As the photon moves through space it's wave shape and frequency oscillate with the waves that comprise space. Space is never a pure vacuum, because of the presence of all these fields and the wave forms of which they consist.

Depending on the density of the fields, the photon can either absorb energy from the fields (and it's frequency increases) or the photon is drained of energy (and it's frequency decreases).

Where one finds matter, one finds stronger fields surrounding this matter. Photons are not drained of their energy and, in fact, they can absorb energy from these fields of energy.

That big gap in the universe is not devoid of all energy. That would be truly impossible and we wouldn't be able to see it, if such were the case. It will still possess certain fundamental frequencies which oscillate throughout our physical universe. However photons probably find the journey across such a relative void difficult because the low frequency field may sap their energy (frequency) level and as a matter of fact, I suspect many photons insteas travel around it skirting fields that, by comparison, have much more strength and pull.

When a radio wave has to pass through a concrete barrier, depending upon the frequency and wavelength of the radio wave, it's progress is impeded somewhat or bounced off the barrier. Photons can experience the same impedance and very strong fields redirect photons just like radio waves.