Takeh, why are most willing to eat inside when being mitztaer regarding rain, but not regarding too hot, too cold, etc?
When you take care of the rain problem, you don't have a sukkah (pashtus), But you can take care of the heat/cold issues and have a sukkah mehuderes.
Also, when it comes to rain the 'גמ gives a clear geder of what's considered mitztaer, when it comes to the other things, it boils down to how'd you react if this situation was in your home.