Because Anaheim needs pitching and not position players, and they want to be able to compete ASAP. That means Cease/Kopech as headliners. They aren't going to be interested in Vaughn as a headliner.
I really thought he was having some lingering lower body pain somewhere, because he wasn't letting it lose with his swing. I said about a month ago that his swing was starting to look good again, and the last month has started to bear that out.
So why isn't the assumption the same for Conforto, you know, to be consistent? Why isn't it about his health? He has shown that he could perform at a high level when healthy WAY more than Kopech and Rodon had after their big injuries.