Why the title? Read it for yourself: American Historical Association Statement on Policies Regarding the Embargoing of Completed History PhD Dissertations. Here's the conclusion:
By endorsing a policy that allows embargos,
the AHA seeks to balance two central though at times competing ideals in our profession–on the one hand, the full and timely dissemination of new historical knowledge; and, on the other, the unfettered ability of young historians to revise their dissertations and obtain a publishing contract from a press
. We believe that the policy recommended here honors both of these ideals by withholding the dissertation from online public access, but only for a clearly stated, limited amount of time, and by encouraging other, more traditional forms of availability that would insure a hard copy of the dissertation remains accessible to scholars and all other interested parties.
I'm going to try hard not to go "Michael Eisen" on this: did the AHA just compare the dissemination of knowledge with careers? It strikes me that if you do scholarship of any sort the discovery and dissemination of knowledge is all, it is the summum bonum. All else is secondary and marginal. As it is the academic job market is brutally Darwinian in the most extreme sense, and more so for humanities scholars. Can you truly push this thread any further by open access requirements for dissertations? I doubt it. But let's test this proposition. Note: I am granting many of the premises of the argument in the statement for the purposes of this post. Even allowing for those premises, when a scholarly discipline goes too far down the careerist rabbit-hole, then it is time for people to start thinking about become actuaries to put bread on the table.