When DH's father died very suddenly, I realised that wills had an enormous emotional component.
As somebody said earlier, they are the last message you get to send to your family and you should make sure the message is unequivocal and non-hurtful (unless you enjoy creating family dramas, which some people do)
In (now) DH's case there was a will that hadn't been signed. That will made some (small, I don't know the details) for him, but none at all for his sister. His father and sister had been estranged for some years.
At the time I made a throwaway remark to DH about how just not getting around to doing some paperwork could lead to such a hassle (the estate went into probate, or whatever it's called because there was no will).
But DH was adamant that it wasn't an oversight that his Dad hadn't signed his will, but a deliberate decision. He believes (and very much WANTS to believe) that when it came to it his Dad couldn't sign a will that left his sister out, despite their estrangement.
It matters a lot to him that the lack of will shows that his Dad loved his sister until he died.
Now you can call that childish and silly. But it's very human. It's very human to want to think well of your parents and have your parents think well of you and your siblings.
To my mind it is extremely foolish and unfair to write a will that treats people you should love equally unequally.