As per Hindu mythology, Garud Puran should not be read unless there is a death in the family. What can be the rationale behind this?

One of the philosophies of Vedanta is that one should always talk and think positive and face adversity like a cricketer right from the first ball he faces. He always thinks he is going to score a 100 till he gets out. Similarly, every person should think that he will live up to 100 years until the last moment of death. Once he dies, he is not there to know how many years he lived. It is only the family who would know this. As far as he is concerned, till the last moment, he had been thinking that he would live for 100 years.

It is true that one should plan his old age and write a will in time but that is for the safety of the family and has nothing to do with your life.

Because Garud Puran talks about death, therefore, it is normally recommended that we do not talk about it in routine life.