Why did alternate timeline Samantha Carter never join the Air Force?

Question

In the episodes Mobius, parts 1 and 2, it seems that the changes SG-1 makes to the timeline hinge on the fact that their part in the rebellion against Ra caused him to take the stargate with him instead of leaving it on Earth to be discovered later.

This prevented the Stargate program from ever existing and as a result;

• Daniel Jackson never joined the SGC (gaining confidence by having his wacky claims substantiated)

• Jack never came out of retirement to go on the first mission to Abydos.

• Teal'c was never encountered by SG-1 on Chulak and convinced to join them.

These all seem fairly logical given the absence of the Stargate but why did Samantha Carter never join the Air Force?

Answer 1

As @brianOrtiz said in his comment, the answer to this is found in the licenced stargate novel Moebius Squared. In the prime universe, George Hammond (knowing that he survived into his 50's and was therefore effectively immortal) put himself at extreme risk in saving Sam's father's Jacob. Her father, and Hammond's example of conspicuous bravery led her to join the USAF.

In the alternate universe, her father died in Vietnam, she barely knew George Hammond and her mother discouraged her from joining the service.

“You remind me of my dad,” Carter said, without thinking.

“Really?” Sam looked faintly embarrassed. “I never knew mine. He was killed in Vietnam when I was a baby. My mom raised me.”

“My mom died when I was in my teens,” Carter said slowly. “Dad took care of us as best he could. That’s part of why I went into the Air Force.”

“Mom would have had a heart attack if I’d even suggested it,” Sam said. “I had the hardest time talking her into letting me get a car, never mind flying a plane. I can’t imagine…” She shook her head. “She was determined to keep me safe. She wasn’t going to lose me like she lost Dad.”

“Did you ever know George Hammond?” Carter asked, and Sam nodded.

“He was my father’s wingman, the one who brought back his body. Danyel said that in your time he commanded the SGC?”

“Yes.”

“I remember when I was little he used to send me Christmas presents,” Sam said. “But Mom didn’t like having him around — too many bad memories, I think. She lost touch. That — I’m sorry about that, from what Danyel’s said. He must have been an amazing man.”

And that was more of what the Stargate had done, Carter thought. The time loop that had thrown the team back to 1969, when they’d given Lieutenant Hammond a note from his future self in order to get back to their own time — she’d wondered how that had changed him, and if it had, indirectly, changed her father. And now she knew. In her time, Hammond had saved Jacob Carter’s life that day in Vietnam, and maybe he had taken a crazy risk because he knew that somehow he was going to survive.

Answer 2

No canonical answer no real way to answer at all with any certainty however the entire premise of alternate timeline is change one little thing and it alters everything that comes after

maybe when the rebellion started early a man who hadnt died before died so his descendants never were born and perhaps one of his descendents said something to a young Samantha Carter that gave her courage and confidence and a desire to serve her country