Board Thread:Questions and Answers/@comment-61.6.238.10-20161107022633/@comment-25322628-20161127030525

His identity was public knowledge because of this fact. As were the other heroes that didn't wear masks. That meant that anyone with the means to kill them or kidnap their loved ones could do just that.

Saitama was the exception because he lives alone and doesn't have any relatives of whom to find.