1. I believe leaving an ideology has more to do with the individual that the ideology, especially when the ideology remains consistent. For example, I was born into a Mormon family, baptized into the LDS church, and even served as an LDS missionary in Tokyo, Japan for two years. Then, I rebelled against the religion, for a variety of self-centered reasons, and demanded to be excommunicated. I remained antagonistic towards the Mormon church for many years. A few years ago, I decided to return to it. During all that time, I was the only thing that changed. The Mormon church remained consistent.
2. In my experience, the LDS church does not take a dim view against its apostates. I was one for many years, and they never approached me with anything but love and kindness, even when they were met with my vitriolic attitude. I have nothing but the utmost respect for the LDS church, and their attitudes towards me during my years as an apostate.
Mormons spend a lot of time proclaiming how much they know it's true to each other. I've always believed this to be some sort of a mental trick like "if we just keep saying it we'll make it so". This isn't to bag on Mormons either. Lots of groups do something similar (many of which are not regions). I have to assume it's an essential part of social functioning at some level.
Someone leaving undoes at least a part of this exposing an underlying crack in the carefully constructed reality. Thus it's a threat. Predictably people don't react well (nor understandably are they comfortable around) threats to their essential world views.
There is a lot to admire about Mormonism. But given the theology it has to be a fair amount of work to maintain belief in the face of modern knowledge.
This probably applies to a lot of more intense religions that take dim views of apostates. Or any other belief systems for that matter (i.e. the Silicon Valley echo chamber with apostate Peter Thiel).