1. When they invested in Open AI it had a more mature board (in particular Reid Hoffman) and afterwards they lost a few members without replacing them. That was probably something Microsoft could have influenced without making themselves part of the problem.
2. They received a call one minute before the decision was made public. That shouldn't happen to a partner that owns 49% of the company you just fired a CEO from.
Sources:
1 - https://loeber.substack.com/p/a-timeline-of-the-openai-board
2 - https://www.axios.com/2023/11/17/microsoft-openai-sam-altman...
Nadella was rightly furious about this, the tail wagged the dog there. And this isn't over yet: you can expect a lot of change on the OpenAI side.