Because it’s not about being a shareholder. It’s about trying hurt Dorsey’s pride. “Watch me destroy your greatest achievement!” Musk is trying to damnatio memoriae.
Dorsey was not part of the lawsuit and in fact rolled over his Twitter shares with the acquisition instead of taking the payout, so again the "Revenge for being forced to honor his word at buying Twitter" theory makes no sense.
That is assuming Muskbis doing this purposely.