I for one applaud them for being cautious.
The real reason they aren't releasing it yet is probably it eats TPU for breakfast, lunch, and dinner and inbetween.
How about "bad agents acquiring dozens of new zero-days and using them to compromise any company or nation they want"? It's not exactly hard to see why you wouldn't want public access to a model significantly better than Opus in cybersecurity.
Also, OpenAI's only real moat used to be the quality of their training data from scraping the pre-GPT-3.5 Internet, but it looks like even they've scratched that too.