It's entirely conceivable that even if AGI (or something comparably significant in terms of how impactful it would be to changing society or nation states) was achievable in our lifetime, it might be that:
1) Achieving it requires a critical mass of research talent in one place that perhaps currently exists at fewer than 5 companies - anecdotally only Google, Meta, and OpenAI. And a comparable number of world governments (At least in the US the best researchers in this field are at these companies, not in academia or government. China may be different.)
This makes it sound like a "security by obscurity" situation, and on a long enough timeline it may be. Without World War 2, without the Manhattan Project, and without the looming Cold War how long would it have taken for Humanity to construct a nuclear bomb? An extra 10 years? 20? 50? Hard to know. Regardless, there is a possibility that for things like AI, with extra time comes the ability to better understand and build those defenses before they're needed.
2) It might also require an amount of computing capacity that only a dozen companies/governments have.
If you open source all the work you remove the guard rails for the growth or what people focus investments on. It also means that hostile nations like Iran or North Korea who may not have the research talent but could acquire the raw compute could utilize it for unknown goals.
Not to mention that what nefarious parties on the internet would use it for. We only know about deep fake porn and generated vocal audio of family members for extortion. Things can get much much worse.