Maybe MS just got extremely lucky, like winning-the-lottery-lucky.

But your timeline is off, however. Their partnership started in 2016[1]. In 2019 MS started to invest publicly in OpenAI - but by then they have had some history.

To me, this is at least suspicious. Granted, I have no hard proof.

[1]: https://blogs.microsoft.com/blog/2016/11/15/advancing-ambiti...