Well yes, that sort of evidence is routinely used to gather evidence and build criminal cases. Emails, like letters, are correspondence between individuals.
ChatGPT isn't (despite it's name) equivalent - the nearest analogy is Google. We know the modus operandi of the world based on these services (incl social media) and privacy is the aspect that's been given up.
Yet no one would think it's acceptable for the NYT and a dozen other news organizations to request an "anonymized" archive of all your emails from provider X, just because said provider is in a lawsuit with them, and you have nothing to do with any of it.
This is shameful, and would create a dangerous precedent. Really hope the order gets struck down.