Why is the average 1 Bar temperature on planets with a thick atmosphere proportional to the distance of the sun?
I will throw out 2 hypothesises to answer the why of the question. Not saying it is true, just saying that it may be valid hypothesises. And both hypothesises don't discount the internal properties of greenhouse gasses.

Somehow positive and negative feedback forces level each other out in the 1 bar thick atmosphere sytems on all 3 planets

There is another overruling equilibrium mechanism, as proposed by Dr. Ronan Connolly &amp; Dr. Michael Connolly, who studied all the weather balloon data.


https://youtu.be/XfRBr7PEawY?t=2506