Doesn't shock me honestly. Persona games generally review well but a lot of people don't like how some of the story beats are a bit creepy/weird. Teachers creeping on students, heavily implied sexual relations between the protag and his teacher, etc so it feels like those games will always be niche because of it.
After playing this, the thing I took away from it is it's essentially Persona, but with a dark fantasy setting. That's generally going to be an easier sell for a wider audience imo.
Combine that with Atlus's JRPG mechanics and you got the probable game of the year.