Its been documented as being the grandest sea faring vessel of all time and to be designed by archimedes. It would seem odd for it to just stay at Alexandria until its end.
From what I can find online it seems that it was made into a building because it was to big to fit into any dock at that time. So I believe that it makes sense for these people to just use it as building .It was also given the name Alexandreia .
You can find more details about the ship here :
https://www.academia.edu/34223271/The_Syracusia_as_a_giant_cargo_vessel