Because it is another step towards approval. It requires FDA to bless the previous data and that confers some additional legitimacy. Further, if the trial design is under the newly created rules, it suggests that the FDA has some degree of faith in the outcome.
When all three trials get started, the odds of success go up significantly, since success on any one trial will lead to an approved drug.That will confer additional legitimacy on the other trials in progress.
Forward progress counts.