GPT-2 was obviously too dangerous to release at the time! It's OK-ish now, when the knowledge that AI can produce arbitrary text is widely shared. It would have been a disaster for scammers and phishers to get GPT-2 at a time when almost everyone still assumed that large volumes of detailed text proved there's a real human being on the other end of the conversation.

And, as we all know, humans can't be scammers. They need the robots to lie.