My Brother and SIL have been trying for nearly fiver years now. Two years ago they decided they needed to destress and focus on something else, so quit their jobs and moved overseas. They've traveled a lot and are living it up, but still no baby.
A friend married at 20 and tried for years before accepting they weren't going to have children, never changed anything in their lives but then surprisingly fell pregnant at 30, had a healthy baby boy but then found herself divorced at 31.
Who knows why any of it happens the way it does, life just isn't fair to everyone I suppose.