The reason behind that is due to how they (most likely) want to tell the story in 2.2. Hildibrand is surprised that his father is now on the Syndicate and at the same time they want you (audience) to be as well.
The one and only flag to trigger the change in cutscene is the hildibrand 2.2 completion. They want the reveal to be done in the Hildibrand questline, not 2.2 main story.
The one and only flag to trigger the change in cutscene is the hildibrand 2.2 completion. They want the reveal to be done in the Hildibrand questline, not 2.2 main story.