Why does 17 seem more popular than 18?

Never got around to playing 18 but from the outside looking in a lot of people seem to prefer 17 over it, to the point modding is easy to come across for 17 while I only see something out for 18 every once in a blue moon. To those that have played 18, I'd like to know if it's just my perspective or if there was an unpopular change between games.