in general as a fan on ntr, vanilla is very boring, if i wanted to just watch two people fuck regularly i'd go into pornhub or smth, with NTR there are consequences to failing or messing up, it makes for more interesting storylines etc. basically the way i see it is if we put it in gaming perspective, vanilla/harem/pure love only games is like giving yourself god mode in a game were you can't lose, while ntr is like playing a game at a harder or hardest difficulty, the challenge in itself, if we go by game with routes that is, some games make it medium - hard to "win" others make it very hard creating a much bigger challenge, and some simply add realism, as if you chase that girl, the others may find someone else, if you chase all of them, they'll get mad when they find out and you lose em all etc.
though i'm mostly a fan of fem protag games, and some "vanilla" games do have a good story such as being a dik