It's different because in the previous antitrust case, Microsoft was accused of product tying. They apparently had private APIs built into their operating syste

It's different because in the previous antitrust case, Microsoft was accused of product tying. They apparently had private APIs built into their operating systems which only their own applications were allowed to use, and weren't available to competitors. There is no such allegation today. Any third-party vendor can write Windows applications that work just as well as Microsoft's own applications. Apple also had a much smaller desktop OS market share at the time. They nearly disappeared but are in a much stronger position today, which makes it harder to argue that Microsoft has a monopoly. There's no strict threshold for market share in these cases, but it's one of the factors taken into account.