Past Simple is more academically accepted rather than Simple Past. Simple Past would indeed sound more natural, however out of the two words "Past" is the core word, while the "Simple" is its attribute, so when we hear someone speak about tenses, it is more convenient for our minds to be refrred to Past first (as more important piece of information) and then to what kind of past - the Simple kind.

 

It can be compared to how herbologists name plants in Latin for scientific reasons - the family comes first, and then the species.

 

My thoughts, anyway.

 

Rather interesting topic, I find.