It has always happened, it just gets talked about now with Internet forums, it is nothing new. You only have to read literature from the past to know it to be true. It is the basis for many stories. Human behaviour and emotions are very complex. In the old days the man always got custody of the children,if the wife left,and you could then be sure that the grandparents lost contact, or had very little contact - it then had a swing the other way and the paternal grandparents suffered. At least nowadays joint custody is sought and it doesn't automatically go one way or the other and it is recognised that grandparents are important to a child, even if it doesn't always happen.
I don't expect that those estranged see any improvement, but overall I think there is some from what it used to be.
We may be more secular, and families more spread out, but you had the same old problems when they were close knit. Lots of women appear to want a daughter to be 'best friend' when older- but it is pure luck whether they turn out that way. You don't get on simply because you give birth. You may be exact opposites or so alike that it causes huge problems!
There are always two sides to the problem and we only hear one and never a balanced view. MN has a 'but we took you to stately homes' thread, which starts a new one as soon as one fills, and it is all about toxic parents. I always think that some of them must be perfectly nice people if you heard their side! (some must undoubtedly be toxic but were they made that way by their own parents?)
If sociologist 'start' researching it there will be a very skewed picture without what went before. There never was a golden age of families living in close and loving proximity! e.g I have only just got in touch with some branches of my family because my grandfather was quite a difficult man and fell out with some of them in about 1900! (And he was a staunch Methodist and lived in close proximity).