Arguing that astronomers can explain the workings of the sun, but that they are clueless of why one layer is significantly cooler than the rest, "like an ice cube", is monumentally in error. If they can't explain that, they can't explain anything.
Nonsense. Since when is knowledge an all or nothing proposition? You can't explain everything about the FE sun, but does that mean that you can't explain anything about it?
The layers are connected to each other. That's why. How is it that one layer is very cold and sandwiched between layers that are millions of degrees? If that can't be explained, it calls into question what is "known" about the physical properties and processes of the rest of the Sun.
Or, are you to claim that astronomers have direct physical evidence for the workings of those layers?
