You care for people if you personally know them. Phil Hughes played a lot of international cricket with almost everybody in the Australian team. Shared the same dressing room.
I don't think the Australian players' reaction is unjustified. In fact, if there were not such a reaction, it would be heartless. For some of the players, he might even have been their best friend.
Moreover, life is never fair. There are so many people who die everyday and nobody seems to care.