I suspect that Scientology may have been permitted to continue in the USA as it allows testing of various mind control techniques, testing that became
difficult for the CIA to conduct openly following the outcry about MK-ULTRA.
After all, they receive preferential treatment from the IRS -
www.youtube.com...
They were allowed to continue even after the conviction of eleven Scientology leaders in the trial relating to the "Operation Snow White" conspiracy
- the largest infiltration of the US Government in history (as many as 5000 operatives were involved).
Other countries have been less accommodating, particularly because of the numerous Scientology policies that encourage criminal behavior.