Umbreon has the mass appeal to the type of people who are furries, if that makes sense. Furries as an archetype seem to like the more edgy looking Pokemon the younger they are and Umbreon is a good mix of edgy but also cute (unlike something like Houndoom which is just edgy). I had a friend in high school who's OC's main Pokemon was an Umbreon, then in college I met this furry dude who wore an Umbreon hat, it just has that kind of appeal to people who are probably into Pokemon porn.
There's also the fact that shiny Umbreon has it's rings turned blue, which is unique among Eeveeloutions and also gives furries a free pass to give their Umbreon OCs whatever color they want for the rings, furthering its popularity.
>>42674886Umbreon predates Glaceon by two generations and is just "cute", where as Umbreon can be portrayed as masculine, feminine, edgy, cute or cool. It's the same reason why Jolteon is so low on the list, it's too difficult to look feminine and can't hit all the angles Umbreon can.
This kind of thing is fun to analyze for me since I do NSFW art.
