I'm no psychologist or sociologist, but it seems that most of the people who treat their kids this way had kids because of external expectations or for status. They treat their kids like property or as an extension of themselves. Raising them to be cis no matter what is not about their child's well-being, it's about how having a trans child makes them look in the eyes of their bigoted, greedy, status-seeking, peers. When their kids come out as trans, they see this as a personal attack on their place in the pecking order.
In general, they treat even their cis children like shit, because they don't think of their children as people, children are just assets in what they think is some kind of cosmic dick measuring contest.
It's incomprehensible because it's pathological and generally sick.
The ship was built as simply as possible and fueled with the precise amount needed for it's weight, there was nothing else to jettison besides the young woman. The plot was intentionally structured around an impossible scenario because the editor of the magazine the story originally appeared in wanted to subvert the "engineer action hero saves the day with a clever idea" trope that was common when it was written. The heavily contrived scenario is the weak point by most people's estimation, but overall the writing is well done and characterizations are very good.
The story bugs a lot of people due to the total lack of any safety margin for such an important mission as delivering emergency medical supplies. A guy named Don Sakers even wrote a rebuttal called The Cold Solution that was meant to point out a few things the original story overlooked without the idea of a bare minimum ship being changed.