Maybe the manifest uselessness of some of those in the humanities can be explained by the fact that they never, or rarely, get suitable feedback. When a surgeon makes a (serious) mistake, a patient dies. When a civil engineer fouls up a calculation, a bridge comes tumbling down. When a vulcanologist prophecies falsely, the volcano shows her up. When a physicist hypothesizes wrongly, the experimental data exposes it. In contrast, an English professor (say), gets no feedback whatsoever from his materials, his subject matter - only from colleagues. And colleagues - unlike erupting volcanoes or a dead patient - can be argued with, dismissed or (seemingly reasonably) rationalized away. As a result, thinking in the humanities can become totally untethered - free to drift capriciously like fads or fashions. The result? Jacques Derrida, Michel Foucault,
Anyway, don't take this too seriously.