By putting it as a matter-of-fact statement (assuming everything else was action packed) there is a massive shift that creates contrast in the piece and leaves a very concise point to shock/leave the reader with.
The event that allowed Collins to pursue her career dreams was
Soon before she finished college, the Air Force started training female pilots.
Explanation:
The space exploration program had been going on for a long time and the man had been to the moon before the NASA thought of training and sending women to the space too.
This changed by the time that Collins graduated which was lucky for her as if it did not happen she would have had to choose a career different from her dreams.
She was chosen for the training program recently started after she graduated and then became one of the contenders for the mission.
Answer:
Because they wanted a better life
