It is that doctor's are familiar with death.
Ordinary people aren't as familiar with death, and don't have a wide range of responses to it because society hides it and pretends it doesn't exist.
The main place regular people encounter death is on the news as a statistic of war and crime. Then when it visits their family and friends, they are unprepared, except for what they know of death, which is a calamity.
Sitcoms don't include death because they exist to take your mind off work, and provide a platform for advertising consumer goods.
Friends and acquaintances don't often talk about death in expansive terms. They only offer a cliche one liner - sorry for your loss - because that's the only response they've learnt. It's a well intentioned sentiment, and also one that's constrained by a fear of death that is unwarranted.
That's a shame because death is an expansive part of life. It's the point at which a life becomes whole, and we can see someone in their entirety. Death, along with birth, is the context for life.
It's going to happen to all of us, no matter how we try to deny it or hide it. Doctors know this and so they let it in. They do this before life descends into the shadows.