It’s not that it’s ignored. It’s that it’s impossible to say ‘it would have been better if xyz happened’ when it didn’t happen.
You can have no idea if life would have been better, had someone’s parents stayed together. It could have easily been a whole lot worse and that the parent who ends the relationship, could see where it was heading and wanted to stop that happening. The kids may have been blissfully unaware, their parents hates eachother, or that their dad was crap and disrespectful to their mother. But would have been aware further down the line. The building resentment could have made the home environment awful after a few more years.
Working on the assumption that life would be better because, as a child, you didn’t realise there was a problem until then doesn’t make sense. Because you have no idea that it would have been better.
Thats like me saying my life would have been great if I won the lottery at 17. I have no idea if it would have been. I might have pissed up the wall, found the pressure too much, got into drugs and be broke or dead now.
If the parents relationship is unhappy the far more likely outcome would be that as the kids got older, the home situation got worse. Not that things carried on with the kids in blissful ignorance of the problems.
I do agree, that the impact of divorce on kids in downplayed. But the kids who are traumatised by divorce are traumatised because at least one of their parents handled it poorly. It’s usually because one (or both) of the adults doesn’t put the kids first. Again, why do you think those parents would have been any better at putting their kids first, if they all lived in the same house?