Just a guess, but I would suspect it's because it's one of the few game genre's that has a nationality tied to it and it probably feels like a box they can't escape -- just because of where they're from.
To them, it's just their own spin on an RPG. No matter how much they change to make it appeal to a broader audience, they're always going to be a JRPG, which feels very limiting. It's always going to be "it's an amazing RPG if you like JRPGs", which to someone making the game probably makes you feel less than. No other country has that.
It's similar to splitting k-pop or even j-pop out. TO people making the music, they probably just want to be considered on a world stage as great pop music. Not just K-pop album of the year.
Even if people here don't mean it negatively, doesn't mean it doesn't feel like a shitty box to people. We rarely apply the same sort of boxes to things from other countries. You don't hear Abba or Robyn are the best S-pop artists of the last 50 years.