I believe the primary drive or one of the primary drives of human beings is connection or the need to feel it, which is pitted against the need to survive, and the conflict of these two needs potentially creates negative emotion. The need for survival and connection also play off each other; for instance, those who are suicidal perceive a future of permanent disconnection. I believe that primarily because of the survival drive, the majority of human fondness for other people and living things is kept in a state of subconsciousness until they die. When someone you know dies, you eventually have strong emotions come around which show you the value you placed on them. Detachment is also sometimes used to honor a platonic or romantic relationship, or keep a relationship closer to its present stability, rather than potentially damaging a relationship with failed attempts at connection, where past experience affects what kind of action or lack thereof is taken.
Where we see fondness through action, we have ignored the possibility of fondness through lack of negative action. The lack of hostility in human inaction can be an indication of fondness; a calmer tone, calmer words, or relaxed body language, can be indications of fondness. A lack of aggression towards other living things in an environment, is always an indication of some amount of fondness in a living thing towards those other living things. We could take this fondness in a radical case, lets say someone was very angry at you, and carrying a gun, but decided to talk to you before pulling the trigger; the inaction of the gunman or gunwoman is space for communication, and I believe the right words, whatever they may be, would get you out alive.
Human beings are inherently connected. They have a solidarity that isn't extended to other life forms, and they have a solidarity which extends to all life. This solidarity likely has to do with sharing genes, in the sense of human solidarity, it is a lesser form of familial solidarity; where the closeness we might feel with siblings is partly because we share genetic makeup, and then also partly because we've grown up with them. In an apocalypse scenario where very few people are alive, we would see loneliness set in to some degree, and people respond to one another in a non-hostile way because of this human race based solidarity, even if they might've been enemies prior to the apocalypse happening.
Although mental distraction plays a role in indifference as well, it doesn't take away from the lack of hostility in human indifference, which shows inherent connection and fondness. Its a threat to our own survival and wellbeing to show too much fondness, but its also a threat to be disconnected because we were too busy trying to survive potential threats. Its liberating to have the idea that love or fondness can be masked in some way by the survival drive because it paints a more optimistic picture of human inaction than that of loveless indifference.