As pps have said, those not having problems don't post needing advice (and that's true of any potential life problem - there's also a high number of cheats and abuse if you don't take that into account).
In addition - people don't generally advertise if they're lc/Nc with people, they just either don't mention them at all - which you probably wouldn't notice, or they feign a better relationship than they do have.
I grew up in an abusive home and my dd was NEVER left alone with either of my parents. But nobody knew this apart from dd. I simply didn't mention it and honestly rarely went out, timing any nights out with sleepovers dd went on or paid for babysitters.
There's a lot of undeserved shame and embarrassment held by those of us that are the children or children-in-law of people like this.
Plus we're very well aware that people from healthy happy families rarely understand and honestly we don't need to hear "oh but it's your mum/dad/sibling how can you never speak to them again" "but it's faaaamily" "but they'd never hurt their gc surely" (why people think this when they've hurt DC I don't know) "surely what they did can't have been that bad" 
yea ok, mum battered at least twice a week, home and belongings broken, constant vile criticism of everyone, leching and sexual abuse - righto not that bad then. Totally safe environment to leave my child in - not!
I for one am glad of the understanding and support of the issues here on mn.
Also in real life (I must have one of those faces) I've actually had quite a few people confide abuse, Nc, not trusting their parents to mind the children until they're older at least due to medical issues or because the grandparents completely ignore widely accepted safety advice eg use of car seats. But they don't tell everyone.