To be fair, technically, you still *could* comment and kudos your own work (AO3 doesn't stop you from doing this); people just don't. I wonder if this is HL-shortcuts exchange etiquette (and that's fascinating to know where the name came from; I had no idea!) running into and being overtaken by general AO3 exchange etiquette, where fake-commenting on your fic to throw people off isn't a thing. Now that you mention it, I do actually remember that happening in the first couple of secret Santa exchanges that I did on LJ in the late 00s (in Stargate fandom, I think); I had completely forgotten about it! It really does seem to have been lost along the way with the move to a more standardized exchange format.