From a doomer/EA perspective, publicly saying that GPT5 is AGI or such would likely inspire & accelerate labs around the world to catch up. Thus it was more "Altruistic" / aligned with humanity's fate to stay mum and leave the situation cloudy.
I suppose maybe there are ones where they are slow-rolling because of their opinions about existential risk of AGI. But that’s not contingent on what OpenAI says or does.