Mature, as in the opposite of ingenuous. It does no good to harm a company further. Kotick did enough damage, he left, all that needed to be said about him was said, tirelessly. Every effort to get him to offer some reparations - expended.
So what was there to gain from the company speaking ill of their past employee? What was even left to say? Nothing. No one wants to work in an organization that vilifies its own people. It was prudent.
I will emphasize again that the morality of these situations is a separate matter from tact. It is very well possible that doing what is good for business does not always align with what is moral. But does this come as a surprise to anyone?
We can recognize that the situation is not one dimensional and not reduce it to such. The same applies to the press release from Open AI - it is graceless, that much can be observed. But we do not yet know whether it is reprehensible, exemplary, or somewhere in between in the sense of morality and justice. It will come out, in other channels rather than official press releases, like in Bobby's case.