As soon as the tooling begins manufacture, it's a heck of a lot more difficult to make revisions. It takes about 2 years from the beginning of tooling manufact

As soon as the tooling begins manufacture, it's a heck of a lot more difficult to make revisions. It takes about 2 years from the beginning of tooling manufacture until the first wing parts touch it (validation testing). And another year or three before actual, meant-to-fly, wing parts touch it. Any changes to wing design risk rebooting the entire process I just described. Additionally, the people doing this work are an extremely limited resource. Major schedule changes disrupt all the future work they previously scheduled. You can't just bring in some contractors to fill in because the work is rather new/novel every time.