For some reason SMT and Persona seem extremely popular. I never played them but I see a lot of fans.
Because they're great games..?
Not really sure I'd call them "extremely" popular though, it's always been a niche series but it's grown in popularity a lot with Persona 4 and especially Persona 5. Think some of that popularity is bleeding back over to SMT now, which is nice to see. Personally I haven't played any SMT games but SMT V looks cool and definitely has me interested.