This is an attempt by Musk to force S&P500 index fund holders to buy SpaceX stock (or the value of it at least). Tesla is currently in the S&P500 because it met the rules to be included years ago. SpaceX does not meet the rules and so was rejected. This is what SpaceX is missing to be included:

• it is not yet GAAP-profitable (reporting a $4.94 billion net loss in 2025)
• it lacks a 12-month public trading seasoning period
• its public free float is too small

This means that Musk missed out on billions of dollars of index fund investor's money when SpaceX IPO'd. A merger with Tesla, with already-registered-Tesla being the acquiring company would appear to skirt the S&P500 rules allowing SpaceX to rake in the automatic index investor money.

I'd personally like to see Standard and Poors (the company behind the S&P500) recognize Musk's attempt for what it is, and deny not only SpaceX after the merger, but kick Tesla out too for breaking the rules.