Here s my guess. On the Earth of this film, it is hard to answer those questions because everything is familiar. Systems have been set up. Things occur without reference to why they occur. Just as a reed flows with the current of Kelvin s pond, the traffic now flows along the city s highways.
Traffic seems as natural as water currents because it exists alongside the other.
It is here and there s no reason to doubt its authenticity. In the same way, the distance between Kelvin and everyone around him seems like his natural state. He doesn t question why he now feels isolated because he thinks he s always felt that way. For him, emotionality is unnecessary, not because it actually is, but because he sees no reason to change the way things are. Once nature takes a certain path, we find it difficult to do anything other than continue in its new direction.