The intellectual property (code, data) was transferred from the nonprofit to the for-profit for about $60M, which is what an independent firm hired to assess the value said the IP was worth in late 2018 / early 2019. The nonprofit itself was never converted to a for-profit, and indeed remains a nonprofit to this day.
The $60M in IP has grown to about a $200B stake in the OpenAI for-profit.
The easiest way to think about this is to globally replace "non-profit" with "tax-vehicle". These things are all kinds of company. They just created the company in a tax efficient (for them) way.
The $60M in IP has grown to about a $200B stake in the OpenAI for-profit.