I'm not saying it's necessarily the right explanation, but it makes sense to me. :P I can tell you as a tag wrangler that the character/reader and character/you tags started seeping onto AO3 a few years ago via those sorts of fandoms and also jrpgs (we had a long discussion as to whether character/reader is the same ship as character/you.) And as a recovering Homestuck fan - you get used to second person pretty quickly if there's a lot of good fic written in it; the "you" stops feeling any more personal than the "I" in first-person, it's just a way of creating a sense of intimacy with the POV character, and it becomes natural to write.

(I'm not saying that you should read the Kylo Ren epics, but there's nothing fundamentally badfic about second person once you've submerged in it enough that it feels natural - when I was really into Homestuck I had to make a deliberate effort to not just do everything second-person.)