> Is it because the government created laws that limited its total discretion?

Yes. As you said, "the people allow for corporations to exist," and the same people created the government and allow it to exist. And when those people created that government they created rules that govern what laws the government is allowed to enact. Those rules are known as the constitution. And one of the first rules the people made when they created the government is the aptly named "first amendment." And that rule clearly states that the government can't take legal action against a citizen for saying something the government doesn't like. The CA government retaliating against OpenAI for its CEO threatening to leave the state would clearly violate this rule.