Government decisions are made democratically, by the people or officers appointed by them, to do what they believe is best for the people.

Corporate decisions are made autocratically, by the owners or their appointed officers, to do what they believe makes the most money.

How is the former not categorically better than the latter?

In theory they are better, but in practice “what makes them the most money” is often “what is best for the people” and governments and elected officials are often inept or corrupt. This doesn’t apply for every government or corporation on every issue, so we need to be nuanced in who we entrust which issues to. Specifically we want to look at the severity of the issue, the incentives, and the corruption and the competence of the government in question.

Because once people are democratically elected or appointed, they no longer are beholden to the people. Once in power, they are free to do whatever they want, which history shows, tends to be pretty self-serving.

It should be. Governments are supposed to represent the people and be accountable to them. Corporations are far too often only accountable to their shareholders. Reality is often different, of course.