He didn't leak the emails because they thought it would make Ben look bad, though Ben doesn't realise how it does, in fact, make him look bad if he ever claims to be impartial, non-partisan, or indeed anything a so-called journalist should theoretically be. It also makes him look bad because it shows just how much he
needs Twitter, at least how it was, so all his bitching and caterwauling about Evil Musk is because it's affected him personally, rather than any allegedly objective complaints he might have about the changes Musk has made.
No, the email was leaked as part of a massive data release of how Twitter worked pre-Musk. This includes this email, where they show they have a close working relationship with Ben as a reporter mostly based on his desire to suck Twitter's dick. It shows a symbiotic relationship between the previous Twitter regime, actively spreading misinformation under the pretense of removing it, and Ben, who has never met a part of the Narrative he hasn't been happy to shill, especially as he benefits.
To Ben, this email shows he's on the Right Side of History. To anyone aware, it's more proof that he's an ideological hack who misses people at Twitter listening to him far more than he would ever admit. That he calls something that was accurate "an insane conspiracy theory" is just the icing on the cake.