Why be a 'general' manager when you can be a specific one? Let's assess the prior Diamondbacks GMs to see which ones might have been the next Connie Mack.
The Marlins did a thing. Specifically, they fired their manager, which is a thing disappointing teams do, and replaced him with their general manager. It's not Ted Turner installing himself as manager level crazy, but it's a very Marlins move. Always keep them guessing!
The why of it is beyond this article's scope, and I'm sure you can read all about it at Edgy Sportsball Website of your choice.