I think Musk (probably using his Saudi admirers yet again) wants to buy OpenAI because he needs a working chatbot right now. For example, he is gutting the General Services Administration and wants to install a GSAi chatbot to replace the workers:

https://www.wired.com/story/doge-chatbot-ai-first-agenda/

Perhaps "big balls" and the other geniuses he hired haven't managed to come up with a working solution.

Musk needs chatbots for his technocracy movement because they are great for faking progress in efficiency without understanding any of the systems they replace and destroy.

He may also need them for online bot campaigns to convince MAGA voters that layoffs, deregulation, H1Bs and supporting billionaires are really in their best interest.

That said, considering he overpaid for Twitter, perhaps OpenAI should consider his offer.