Why isn't the subjunctive ("that she be") used in "He insists that she is crazy"? [closed]

The insistence of the first sentence is qualitatively different from the second.

In the first, he is insisting that something should happen in the future. This requires the form of the verb which can conveniently be called the subjunctive.

In the second, he is insisting that something is true in the present. This requires the normal indicative form, which is why we say "He insists that she is crazy."

To say "He insists that she be crazy" is to insist that, while not crazy now, it is necessary for her to be crazy in the future. It's highly unusual for someone to have to go crazy.