From time to time there would be a few letters from the bank for her father, but then he was not a normal father. Sophie’s father was the captain of a big oil tanker, and was away for most of the year. During the few weeks at a time when he was at home, he would shuffle around the house making it nice and cozy for Sophie and her mother. But when he was at sea he could seem very distant. As a native speaker and in your view, what it can be the reason why her father could seem very distant or preoccupied?
He is preoccupied with tasks that won't able him to communicate with her daily and his ship is very far away...distant.
Circa 100 deaths per year occur on tankers (which doesn't include delayed victims who succumb later to cancer and other chemical-related illnesses). Any captain with many years of experience and zero casualties during that span earned it by not being distracted from duties to ship / crew and staying current with stringent safety standards. While unscrupulous practices and fake marine administration certificates are on the rise, the most respectable companies still invest in ultra-serious ship management training that requires their officers to be heavily "preoccupied" with making successful cargo journeys and taking responsibility for safe tanker clean-ups.