These models are capable of generating photorealistic child pornography. That's why they're not being released.
I have no evidence to back this up, other than anecdotal. All the hand waving vague posts from SD, DALLE etc read like PR tactics to avoid getting the spotlight from the media and governments.
No one wants to post about this but I think everyone knows it's true, as soon as Congress realizes what these models can be used for there's going to be a moral panic.
EDIT: All of the replies are assuming I'm saying this is a good reason for not releasing these models. I don't say that anywhere nor do I agree with it.
You should strive to respond to the strongest interpretation of what you read and not the weakest one.