After reading news accounts of the young man's past, it's possible that he never really wanted to be a pilot at all.
He had a high-achieving, financially successful German father with whom he still lived part-time and who was probably paying for the young man's apartment. The piano-teacher mother is barely mentioned - while the son was running half-marathons with his father.
Perhaps the son was always trying to meet his father's high standards. Maybe that's why he "burned out" during pilot training - he may have hated flying. He didn't really want to be a pilot, but knew that "Tomato Andy" the flight attendant, couldn't possibly meet his father's lofty expectations.
He was reportedly having relationship problems - going on holiday in Miami with a male acquaintance; then living with a girlfriend in the apartment.
Inside, this young man might have been a totally different person who hated the life he felt he had to live outwardly. Perhaps his final desperate act was to kill his public persona......