There are many advantages to making your working papers available on-line. It allows you to get feedback, it creates exposure for a paper, and it allows you to take credit before the time consuming journal publishing process finally lets your paper see the light of day as an Article. Theoretically, all of this would work best if there were one system where all these papers are stored. Indeed in law and in economics everyone seems to have converged on SSRN as that place.
Not so in political science. The creation of the political science network has made SSRN more popular but it is still used quite sparingly. Instead, political methodologists post at the PolMeth archive, APSA conference goers at the APSA archive, MPSA participants at the MPSA archive, ISA participants at the ISA archive and so on. It is not just expensive for all these organizations to maintain these archives but it also creates inefficiencies in the dissemination of papers. For example, Google Scholar does not search all of these archives. Moreover, it is not always easy to update these papers after a conference participation. It also likely leads to multiple versions of the same working paper, making it difficult to determine what the most recent version is.
I can think of some good reasons why this persists. For example, PolMeth is a pretty closely knit community who would like to keep up to date with what people within that community are doing. SSRN allows you to set up your own communities but these get “contaminated” quickly. For the most part, though, I suspect that internal organizational dynamics are responsible for this. Or is there something about SSRN that I am not getting?