Answer Choice B?

You're looking for the phrase that accomplishes the same thing in each passage. In passage A, the author is talking about the flaws of historiographical writing which he or she distills down to the phrase "scholarly monographs that sap the vitality of history." In other words, the problem of historical writing is that it's boring. In passage A, the author is talking about the flaws of legal writing, which he or she distills down to (B) "Conformity is a virtue...". In other words, it's boring. Both are somewhat snarky phrases that sum up the author's opinion of the genre of writing before launching into a larger discussion. The other phrases offered as options don't serve the same purpose as the listed phrase from passage A.

why not e?

E is a suggestion of a correction, whereas what you were looking for was a direct description of the flaw each author perceived. So, I'm sure Christopher will correct me if i am wrong - but i go through the answer choices (again looking for description of the flaw) as: A - generally just an introduction, they put this here, and want to fool you by it's POSITION in the argument (up front) not it's function. B - spot on, right answer, it's the only answer that describes the perceived problem directly, even, if as Christopher said, it's a wee bit snarky. C - just a description of how things are, perhaps a description of how the problem is CONTINUED, but not what the problem is D - this is a description of WHY the suggested correction is needed, not what the problem is. E - sort of a description of the author thinking how little thinking might have to change to start making progress, certainly not a criticism.