I've left a church twice, for two very different reasons.
The first time I left a church it was reluctantly but because I was moving out of the area, far enough that ongoing attendance was no longer an option. I still stay in contact with that church and technically I think I'm still a member.
The second time I left a church it was because it was riddled with toxic theology. They preached a message of prosperity but couldn't pay their bills, they preached guaranteed healing in Christ but suffered just as much sickness as anywhere else, they spoke endlessly of the revival they were convinced was coming despite steadily falling attendance, and every which way I turned there was more and more bad theology from places like Bethel, more and more following of false prophets, more and more butchering of Scripture to make it say something it was never meant to say and so on. If something didn't align with Scripture that didn't cause any problems there, if it directly contradicted Scripture nobody seemed to care because apparently it "felt right" to them (whatever that means). During their regular "open mic" times there was a guy there who would preach his own mini-sermons that often ignored or butchered Scripture, and when he said something along the lines of "yeah, yeah, I know what the Bible says but I met a guy in an elevator who told me...." I had a couple of long discussions with the minister to express my concerns and it gradually became clear nothing was going to change. One of the council members was concerned about why I was leaving so I expressed my concerns to her and explained how I thought the teachers they were following were building the kingdom of the antichrist. Sadly she was too busy to address my concerns, or even to reply to the email she asked me to send her. There's no way I can stay at a church that causes me that level of theological concern where they won't even answer my questions.