Biblical Hebrew consistently uses the letter ס (s) to transcribe names with the Akkadian consonant š. For example, Esarhaddon for Aššur-aḥa-iddina, Esther from Ištar, Sargon from Šarru-ukīn (all Akkadian transcriptions copied from Wikipedia). Etymologically, Akkadian š and Hebrew š almost always correspond (š and ṯ, although Akkadian š can also correspond to Hebrew ś, but not to s to my knowledge).
The only exception I can think of is Aššur which is transcribed that way (with š). Since the Aramaic reflex is Attur, the word seems to have reached both languages as a descendant (through *Aṯṯur) and not a borrowing.
On the other hand, Shalmaneser comes from Šulmanu-ašarid, and yet preserves the š at the beginning of the word, while the second š is transcribed as s.
My question is: Why does Hebrew not transcribe Akkadian š with Hebrew ש (š) instead of ס (s)? Does this indicate that Akkadian š was actually pronounced s (maybe only in Assyria)? And why was the š preserved in the name of Shalmaneser (only one of the two times)?