On RfM the theory was put out there that the church is suffering a brain drain as it's most intelligent see the truth and leave. I don't know about that. It might be true. But at least in my wife's ward the members seem to be pretty well-educated, intelligent, and successful. After I left a couple of members let me know that they didn't really believe. I never imagined that when I was active, but now I look back and think that many of the most active members were probably cultural mormons or New Order Mormons who didn't literally believe the church's teachings.
The problem is, people aren't inherently rational. A lot of our choices and beliefs don't have a foundation in rational thought and logic and evidence. In fact, it's pretty clear that humans are very bad at logic and evaluating evidence to reach good conclusions. It takes years of education to train people to be logical and impartial in reaching conclusions and even then they are very error prone.
Also, very intelligent people can be very good at rationalizing or coming up with very creative justifications for their beliefs. Those rationalizations don't have to be likely or probable, but as long as they are remotely plausible then people will cling to them to justify believing what they want to believe. To a true believer, the implausibility just further confirms that it must have a divine, miraculous origin. To quote the Hinckster, "Isn't it wonderful?"
Look, people believe what they want to believe and if it gives them comfort then they will cling to those beliefs. The church has very effectively set up an environment that severely penalizes non-conformity and non-belief to the extent that most members are unwilling to even consider the possibility that the church is bull until after they become disenchanted with the church for whatever reasons they have. In other words, they are open to disbelief once belief is no longer comforting for them. And in the case of the church, once you allow yourself to consider the possibility, it quickly becomes pretty obvious what a load of bull the church teaches.
So, in the same way the missionaries prey on people who are having difficulty as potential converts, it's probably best to refrain from deconverting your TBM friends and family while they are content with the church. They'll only be open to considering the question if they are discontent with the church's product.
Ironically, I think that the biggest common denominator that former Mormons share it is that they come to a realization that the church isn't meeting their needs. In other words, continued belief doesn't bring comfort and may actually be creating a lot of discomfort. At that point the consider whether it's worth it to continue believing and are more open to questioning. The best thing the church could do to stop the exodus would be to provide a better product and make sure that their members are satisfied. Instead they are becoming more insular and controlling and driving more people out the door.