Although even the piece notes that sometimes people are just shitty, sometimes the reason isn't that the estranged did something wrong. And in that case, the estranged could genuinely not know.
And that those who know don't hang around forums like the ones mentioned because they aren't helpful. If you know why someone is estranged from you and you can articulate those reasons, you go to a place that deals with those reasons.
Although I'm curious what prompted you to post this.