Like the days where it seemed like everyone maintained a Blogger site and wrote longer form content?
Maybe it's more because blogging was a fluke to begin with. Kind of like in my junior high (2002?) every kid had an online journal (Xanga) that died when we moved to sharing those thoughts on Myspace.
Maybe it could be seen is more of a ephemeral shared "mass-delusion" that we should maintain blogs and post our thoughts online about favorite topics. (Hmm, I think this seems very reasonable.)
But moving to social media doesn't seem to explain everything. People had long form blogs about all subject you could think of. And it's not like it was obsoleted by posting those thoughts on Facebook. Instead the idea of individuals posting their long (text) thoughts on hobby topics just seemed to almost die completely.