It's to dodge liability for any suits from people this story implicates. A lot of these former employees could argue that Elon's position allows him to make it impossible to ever work again. Seeing how Elon just fired them, it also implies he did so out of malice, regardless of any severance packages they may have accepted.

By distancing himself in this way he quite simply protects himself from a bevy of disgruntled former Twitter employees. If you look back to Johnny Depp's trial and his use of Adam Waldman in order to tell his story to independent journalists/creators, you get some idea of how offloading your story to someone can put a damper on anyone trying to claim you defamed them.

That's just the obvious reason, however. Musk probably has other reasons in mind, looking forward into a future we can't see because we don't even know the pieces in play on the board yet.