>>16309788Xenophilia the word you're looking for is Xenophilia. A lot of people fancy the idea of screwing other intelligent lifeforms. Arguably, about half of the people who even like the more feral looking Pokemon are actually more this than the other fetishes Furries are associated with.
Also to answer your question OP, the design is nice, it's pretty and it's the empathetic type of psychic which makes it popular from a lore and design viewpoint. People like to sexualize things they like in an emotional way or find pretty (but not entirely sexy), human behavior can be weird like that. It's also one of the fairies that isn't a pink blob.