Doppler shift is easy to understand.
No one seems to understand the cause of gravitational light frequency shift(red or blue).
The answer is in GR but I have never read the answer in words that I can understand.
Maybe it is lost in the incomprehensible maths that is given as an explanation by
people who cannot visualize the reason.
Soon, I think I can make someone explain it to me by asking the right questions.

Why not just say it?.
Because it will be rejected (one more nut on ATM)with little thought but is simple.
It also explains the missing mass without inventing dark matter.

Answer my questions and you will say the answer.