At some point in the process, there is a worry that Musks public statements about buying Twitter when he owned like 10% and then not making a real effort to do so may have been investigated as a pump and dump (especially if he followed through in his threat to sell his stock if he wasn't allowed to buy it).
Now, I would say that was maybe a month of a long process when that was true.
Musk's apparent thinking was that it would have been easier to wriggle his way out of the Twitter purchase than the fines (around 1bn, if I recall correctly)
You do need to buy Twitter to avoid running afoul of the SEC.
You do need to buy (something) to dump lots of Tesla stock without cratering it.