One left because women couldn’t be ordained priests and became an atheist.
Another left due to bad experiences with a priest. He goes to the protestant church with his wife when they both feel like it, but he won’t come back to the Catholic faith because him and his wife never want to have children so the contraception issue is a problem, then his family member is in a gay marriage, and one of his family’s friends has decided he is no longer male and transitioned. So A LOT would have to change in his life if he accepted the faith of his childhood again.
My brother left because he saw mass as just some man standing on a stage dictating at people as we droned and chanted back without actually knowing what they were saying. He says as long as he lives a good life then he will satisfy God.
Another left because he saw no use for it anymore and it was just a bunch of rules.
Another left because he was raised in a Hindu/Catholic home and his Catholic religious education told him that the Trinity was a metaphor for the different energies in the world like rock energy, tree energy, air energy, etc. Then when faced with such confusion he just decided science had more rational answers than the mix he was getting.
So yeah, I can’t stretch my arms out around me without finding someone who’s left the Church. Most of the ones I meet haven’t joined another denomination though. They just stopped with any type of religion in general while some just think of it around Christmas/Easter time.