I'm surprised that you don't mention the humanities as a really bad case where there is little low-hanging fruit and high ideological content. Take English literature for example. Barrels of ink have been spilled in writing about Hamlet, and genuinely new insights are quite rare. The methods are also about as unsound as you can imagine. Freud is still heavily cited and applied, and postmodern/poststructuralist/deconstructionist writing seems to be accorded higher status the more impossible to read it is.

Ideological interest is also a big problem. This seems almost inevitable, since the subject of the humanities is human culture, which is naturally bound up with human ideals, beliefs, and opinions. Academic disciplines are social groups, so they have a natural tendency to develop group norms and ideologies. It's unsurprising that this trend is reinforced in those disciplines that have ideologies as their subject matter. The result is that interpretations which do not support the dominant paradigm (often a variation on how certain sympathetic social groups are repressed, marginalized, or "otherized"), are themselves suppressed.

One theory of why the humanities are so bad is that there is no empirical test for whether an answer is right or not. Incorrect science leads to incorrect predictions, and even incorrect macroeconomics leads to suboptimal policy decisions. But it's hard to imagine what an "incorrect" interpretation of Hamlet even looks like, or what the impact of having an incorrect interpretation would be. Hence, there's no pressure towards correct answers that offsets the natural tendency for social communities to develop and enforce social norms.

I wonder if "empirical testability" is a should be included with the low-hanging fruit heuristic.