It just makes more sense to build it in an entity with better funding and commercialization. There will be advanced 2-3 AIs and the most humane one doesn't necessarily win out. It is the one that has the most resources, is used and supported by most people and can do a lot. At this point it doesn't seem OpenAI can get that. It seems to be a lose-lose to stay at open AI - you lose the money and the potential to create something impactful and safe.
It is wrong to assume Microsoft cannot build a safe AI especially within a separate OpenAI-2, better than the for-profit in a non-profit structure.