The main speculation is that Tin tower sounded a lot like twin towers, and following the 9/11 attack in the United states and the fact that one of the twin towers burns to the ground in the backstory, they didn't want to risk it the connection. Also, the Japanese name, Suzu no Tō, can translate into "bell tower" or "twin tower." It's possible that they thought bell would be more appropriate than tin though.
