And then, there are different situations. Always, we call it like we sees it, as we experience it. I have a friend who works in the final arrangements world. He reports that it is not at all uncommon to find that there are situations in which a parent and child have not spoken to each other in many years.
I know if you have a happy relationship with your family and no step parents, jealous siblings and those types of issues you tend to think in terms of your situation and think it would be dreadful for parents to do something like this, have bad feelings toward parents who intentionally "hurt their children." Then there is the rest of the story.
There are several cases of children who have very deliberately hurt and used and taken advantage of their parents through the years. There are adult children out there that you'd perhaps have no problem disinheriting. Perhaps back in the day, you spent untold amounts of your money, time and tears on rehabs or lawyers or bills paid for this child and feel he's already had "his share." Perhaps the parent finding happiness after the mother passed away has really upset the adult child. Maybe he has gone out of his way to let his father know that he still expects to inherit and made it amazingly plain that the reason he wasn't happy with the new relationship is that he doesn't give a rat's behind whether Dad is happy or not, he just wants "his share" of the money he's expecting.
One of my siblings called me, not to congratulate me after my wedding, but to demand I set up some sort of trust to make sure my share of the family land stays in the family and his children inherit it, even if I am now married to "this yahoo!" Yes, some family members are easier than others to leave out completely. So many people in difficult family situations die intestate. This father went out of his way to clearly make a will and state his wishes. His other children have accepted them. They know the circumstances. I do not have a problem with a person being able to leave his money anywhere he wants to, not necessarily to his adult children. This is not an Anna Nichole Smith situation where this "young vamp" has distorted this man's thinking when he was addled by old age and/or dementia. This is possibly a case of someone who found a happy relationship with a peer after he was widowed. The children who bothered to come around, perhaps get to know her, are all right with the distribution of his wealth.
Incidentally I am sole beneficiary of my husband's will, as he is on mine. We both have children by previous marriages. We fully understand how the other person feels about their children and their relationship with them, and have a non binding agreement about what we'd like to have happen later. But then, as the attorney said to both of us "You could take everything and run off to Tahiti with some twenty year old, you know!"