I have another theory: Quantum Mechanics proves that particles form and annihilate each other in vacuum space. This process would create a slight "resistance" to the travelling photons and cause dispersion over distances of billions or trillions of light years, effectively causing energy loss and therefore a frequency shift. None of the astronomical simulations account for this Quantum Mechanical effect.
Virtual particle/anti-particle pairs popping in and out of the vacuum over tiny time scales don't interact with light. Only real particles do.
If they did, because there'd be many charged particles, they would scatter enough light that we wouldn't get clear views of very distant object. That is, the universe would be partly opaque rather than transparent, and this would increase with distant. This is not the way the universe appears.