According to the Wikipedia entry on the USS Little Rock...
"...a boiler room casualty occurred during the summer of 1976 while she was cruising in the Mediterranean. A field survey revealed the ship's propulsion system was in a significantly dire material condition and would require extensive and expensive overhauls and repairs. Given the ships age, only minimal repairs were made to allow the ship to transit back to Norfolk, VA. Further survey inspections were made, however it was decided that the ship would decommissioned in the fall of 1976. A year later the ship was towed via the St Laurence Seaway to Buffalo, NY, where she resides thru to today as a museum ship."
Plus, the TALOS Surface to Air Missile (SAM) System that was the Little Rock's main armament was decommissioned Navy wide in the Spring of 1976. The engine room incident and the projected cost of modernization sealed the Little Rock's fate and she was decommissioned and donated to the museum.
I have the utmost respect for anyone who "sailed in harm's way" in either surface ships or submarines. There are no open spaces (unless on a carrier or above decks) in ships. If someone decides to shoot at you there's no place to hide and ships nowadays have no armor to speak of. Being stuck in a "sardine can" for months AND being underwater? Do I really need to explain?