I doubt Microsoft is dictating terms here. I think the scene is many organizations competing for the opportunity to supply OpenAI’s compute. And OpenAI making choices based on business, technical, and political considerations.
So while they don't have anyone actually on the board, they do have quite some leverage.
Edit - last year, Microsoft quit the OpenAI board https://apnews.com/article/microsoft-openai-artificial-intel...
I think Microsoft’s shares don’t have voting power.