In a lot of big coporat-ey places, there is a very restrictive retention policy due to legal reasons.
If your stated IT policy is that "all mail is automatically deleted after 3 months" then that reduces your risk to discovery procedures. And since it is a published, global policy, you cannot be held in contempt of court of prosecuted for destruction of evidence.
I actually have a very hard time believing that a court is going to find that a company that only retains emails for three months isn't doing something like engaging in spoliation.
On the flip side I have never worked at a company that did not have retention policy. This includes startups and large corporate companies. Retention policies are pretty common.
> The rest allegedly fell victim to the E-Mail deletion policy at OpenAI.
I have never worked in a place that deleted emails. And OpenAI is not even that big or old. I suppose I am not surprised.