I’m sure you graduated at the top of your law school class but the Supreme Court said absolutely nothing about Twitter’s responsibilities to anybody. They’re a private company and can do what they want.
Actually the Supreme Court didn’t rule on it yet.
Twitter may be a “private” company but they’re now ordered not to let Trump block users because Trump is a public official so much for “private company” that can do what they want. (You may have also read that Facebook and YouTube recently announced that their rules of conduct do NOT apply to government posters - that’s a direct outcome of this ruling)
Third - again - it’s a legal precedent that the courts found that government users on private systems are de-facto government operations - that has fallout and real legal side effects even if the ruling didn’t discuss them.