This is
a good question.
Sectarian and new religious movements enjoy only a very modest amount of success in recruiting and retaining members in the U.S. If there is a secret mind control technique at work, it is not a very good one. The only realm in which sects and NRMs are wildly successful is urban legend.
Here's a thought experiment:
Give your best and most liberal estimate of the peak number of Moonies (a/k/a Unification Church members) in the U.S. in the last fifty years.
Most people will guess that it is a number over one hundred thousand; in fact, Unification Church membership peaked in the 1970's at around ten thousand, and that included Unificationists from Korea and Japan who had married U.S. citizens and came here to live.
Since then, membership has fallen off and stabilized somewhat, but attrition rates for new members were always high. In fact, this is one characteristic shared by a number of high profile but otherwise dissimiliar NRMs.