Most people don't realize that Cruise (and about every other celebrity that praises Scientology) is probably being blackmailed into doing all his shit by the so called "Thetons" of Scientology... Whenever you become a Scientologist, you have to confess, or "Audit" yourself to some of these guys, but instead of having a confessional canon, where the information can't even be revealed by court order, these "Thetons" can tell anyone they want.
Celebrities tend to do stupid, illegal, career ending shit, and as part of their "Audits" they reveal these things... Perfect blackmail material, so when said celebrity wants to leave the cult'church', they really have no choice but to stay.
Scientology has a looooong history of blackmailing it's followers.