Because the air force head thinks that "as its stealth then it will be invulnerable but the A-10 is slow and easy to shoot down". This is the entire line of thought.
Or Terry Prachett offers the idea that it would cause time to diverge, a trousers of time with the original in one leg and dimension and the alter in the other. You would be stuck the alternative though. This way both events happen.
Because I loving creating paradoxes for some reason. In fact, why don't you invent time travel and shoot your grandparents before your parent are born. The results are fun.
You can't have on topic or off topic in the off topic as any on topic would automatically become off topic and any off topic would be on topic so you're stuck in a infinite loop. As a result there is no on or off topic, just The Topic.