The board governs a mission-driven nonprofit, not a profit-focused enterprise where Microsoft has board-level influence as investor. This tension (operating as if it is a startup when it is not) is why Altman was fired.
Stakeholder is not a by-word for shareholder. Microsoft has a very large stake in the outcome of OpenAI’s decisions, even if they aren’t a “shareholder” (if that were a thing) of the OpenAI non-profit.