I read once the George W. Bush wrote a personal letter to each family of a serviceman killed in action.
It’s a nice tradition but certainly not a requirement of the POTUS. Imagine if Roosevelt or Truman tried that. It would have been impossible for even Johnson.
Roosevelt would have had to write a letter or hold one phone conversation every six minutes to keep up with the death notifications during WWII. No time off for sleep or potty breaks. Maybe he died of writers cramp.