If you read the stories of (too) many exmormons, many become atheistic as a reaction to the discovery that their faith is false and do not want to have anything to do with ‘god’ anymore.
There is also the constant brainwashing from childhood on that “if the LDS church in not true, then NO church is.”
If I lost faith in the Church I would certainly have to re-examine my belief in God as well.
I think that a lot of people who leave do so after dismantling in their minds the great events of the restoration. A common result is that those people look far more skeptically upon the events of the Bible and the establishment of the original Christian church.
...I have seen that an awful lot of people who leave the church seem to tend to also leave organized religion altogether. Many are agnostic. There are those who leave and attend other churches, but they are at least anecdotally the minority.