It's because they are not. An Rpg is not a jrpg just because it's made in Japan. JRPG refers to a very specific type of game, turn based largely linear. Final fantasy, Dragon Quest, Chrono Trigger, Octopath Traveler, etc etc. That's what most people think when you say JRPG and if so they would be right to say that they like or dislike the genre. This is a non issue as usual.

I'm not sure how you classify a western RPG versus a JRPG, but the thing that stands out in my mind is that those games are full of elements that commonly define each of them, and that makes sense, given the lineage of each branch of "RPG". Western RPGs stick closer to tabletop stuff, as that's what developed in the PC scene. JRPGs started out that way, but whisper-down-the-lane and iteration on what they'd already made tended to make different characteristics more prominent. So Miyazaki was likely more familiar with JRPGs, but he's also said that he was inspired by the difficulty in understanding English D&D, which is why Souls games feel so much like both western RPGs and JRPGs.

Because, what no one wants to admit, it was used to specifically call a text heavy game with no skill required. It's very clear it was used derogatorily when a game the "hardcore's" likes comes from Japan and you are playing a role and it is lore heavy, "oh but it's not really a rpg" uh huh...