Unless I'm missing something, this stands to reason if you don't work there.
Kinda like how none of us are privy to anything else going on inside the company. We're all speculating in the end, and it's healthy to have an open mind about what's going on without preconceived notions.
It's also possible that the structure of the non-profit/for-profit/operating agreement/etc. just isn't strong enough to achieve the intent and the investors have the strangehold in reality.
If I was invested in the mission statement of OpenAI I don't think I would view the reinstatement of Altman as a good thing, though. Thankfully my interest in all of this is purely entertainment.
Optics matter a lot, even for non-profits, especially for non-profits nominally above a for-profit. Check out their corporate org chart to see how it all hangs together and then it may make more sense:
https://openai.com/our-structure
Each of the boxes where the word 'investor' or 'employee' is present would have standing to sue if the OpenAI board of directors of the non-profit would act against their interests. That may not work out in the long run but in the short term that could be immensely distracting and it could even affect board members privately.
Now we either see a belated - and somewhat erratic - response to all that went before or there is some smoking gun. If there isn't they have just done themselves an immense disservice. Maybe they think they can live without donations now that the commercial ball is rolling downhill fast enough but that only works if you don't damage your brand.