>If any other politician can block people from their accounts, why not Trump?
Because he is using it to announce government policy.
Suppose he has another twitter feed that announces tariff increases, tax cuts, new bans on certain companies etc. a few days in advance - but this one is private, run by Trump and available for a mere $M donation.
He has already announced government economic statistics on his twitter ahead of official releases, so investors that follow his twitter feed have a theoretical advantage over any that don't (although possibly face higher mental health medical costs)