Yeah, that's definitely a common reason. But I actually feel that it's one of the worst ones, and that kids would be much better off if the parents calmly explaining their decision to the kids in a positive way, thereby sparing them the pain, conflict, and at the very least unhapiness that staying together would likely bring.
Some kids need two parents more than others. My ex and I stayed together as long as we did in part "for the kids." He physically moved out about a month before our oldest turned 18. I think we did the right thing. I have health problems and two special needs sons. My oldest was quite challenging to raise. I have reason to believe that divorcing sooner would have been catastrophic and potentially deadly for one or more of us.
Since you cannot a/b test this in individual cases and can only say "people who left earlier have these corresponding average experiences or outcomes compared to people who stayed longer," I think it's a terrible disservice to many people with big life challenges to act like they were just being neurotic to stay as they long as they did.
My comment is intended to be taken broadly on average. Based on what you say here, I would agree with you that staying married might have been a better choice in your specific situation.
