Partly the self-consciousness lies in a distrust of authority, both that of the author and of the sources which the author is relying on, so that readers want to question for themselves - we are acutely aware of the possibility of 'bias', even if many readers think of it rather too simplistically (for or against when it is often more complicated than that).
And partly there is an element of intellectual fashion here - the success of writers bringing their own search for the evidence into the story has had an influence beyond simple imitations. For a while it looked very new and exciting, although its antecedents actually go back a long way, including works such as The Quest for Corvo and even Boswell's life of Johnson. I suspect that that fashion has actually begun to fade, and that there is a renewed emphasis on looking for an individual story which can be made to illuminate a wider picture and will - if well told - appeal to a wide readership. One can think of dozens of really excellent examples of this in the last few years such as Longitude, the Surgeon of Crowthorne and Rifles. Not all subjects are susceptible to this treatment, but it can work wonderfully well.