I agree that most, but not every estranged parent is part of the problem.
I am estranged from my daughter, but this is not a defensive mother speaking. I had no idea, for many years, why my daughter suddenly cut contact not only with me, but with my whole family including her siblings, her aunts and uncles, cousins, grandparents etc. She immediately changed her phone number and moved house to an undisclosed location.
And I had absolutely no idea why, and no way of asking her.
Fast forward a decade, and a couple of years ago my sister told me the reason my daughter had estranged herself; my sister found out some time ago, but had kept it to herself. As I had been certain of, she confirmed the estrangement was absolutely nothing to do with me, but related to a single member of my extended family (not my sister). My daughter had done something that was very wrong and rather than face the problem she literally 'ran away'.
It's been well over a decade now and while I don't agree with the action my daughter took at least I understand it, and I do have a great deal of sympathy for her situation. I think her decision to cut all contact was the worst one she could have made, but it would have required extreme bravery on her part to face the family and expose her actions and their consequences.
I am sad that my beloved grandchildren have grown up without the extended family that love them, and I'm sad for myself - I love my grandchildren very much and I have been unable to continue the close relationship we had until the estrangement.
I eventually found one of my grandchildren on various social media and for some time was able to observe them discreetly, and I am pleased that the information I gleaned is reassuring. Some family members (who still don't know the backstory) have urged me to make contact, but I have declined as I think it is unfair to do that. My daughter seems to have been a good mother, but I have no idea what she told her children about distancing herself from the family and I have no wish to jeopardise their relationship with their mum. I can be found if my grandchildren wish to find me.
I'm writing this because I really did know that I hadn't done anything to precipitate the estrangement, and yet time and time again people assumed I must have been at fault and that I was in denial, and I even began to doubt myself. I suspect my situation is fairly unique, but just in case there is someone else who genuinely, unreservedly believes they did not contribute in any way to the estrangement I thought it was worth explaining that, exceptionally, it can be the case.