I read several questions/answers about red shift on this web site, but there is something I still don't understand.
Why is red-shift considered to be the effect of expanding space-time, why it could not be a change in the speed of light. After all, if the speed slowly increases, it could affect the wavelength of the light. And perhaps something else we call "constant" could be changing and affect the wavelength of light. I don't understand why space-time would change but no other physics constants or even laws.