If I remember that correctly, for a while they were all over the place; a specific series I remembered particularly well was in Pre-1900 and Post-1900, but I suppose many others would've been in Chat.
The former series went down fairly normally IIRC; presumably (it would've made sense) at some point in mid-2012 the latter group was perceived as filling up Chat and moved to Books and Media, where they stayed happily for several more months.
Meanwhile, a separate issue led to the banning of polls from Chat. I don't recall the exact details, but I don't think it involved retrospective elections in any way.
Fast-forward to December 2012, when retrospective elections got a new surge of popularity. Now they are perceived as filling up Books and Media, and are moved to Chat (if my assumption that they were originally from there is correct, that would've been a bit ironic). As polls are already forbidden there, external polls have to be used; this was basically the original discussion in this thread.
Ultimately, in January 2013, the newly Chat-based series died out; in March or so, a new one was created (Election Day), and now it was based in SW like it should've been in the first place
Okay, admittedly, back when it all started, SW effectively meant Sandbox, which made it that much more isolated - and had some other negative effects as well (I made a mental list but forgot it); since the reorganization, this isn't much of a problem, and the election series are a healthy fad again - which I hope they remain long enough for the current ongoing games to get at least to the 2010s