Because the other definitions unfairly pigeon-hole any RPGs made in Japan into the category of JRPG even if they don't fit the typical style of JRPGs.
The only pigeon-holing going on is this kind of thinking that doesn't allow genres to evolve. It's basically saying that any JRPG that isn't a throwback to the 90s somehow isn't a JRPG any more, allowing us to say that they never change. We wouldn't say that CoD isn't an FPS because it doesn't have your health as a percentage and wide levels to explore like in Doom, or other old-school gameplay mechanics, so why limit JRPGs to what they were?
In the last gen we saw a mix of turn-based, action and hybrid combat. A mix of battle screens and on-field enemies. A mix of cinematic cut scenes vs small budget productions, and a mix of combat styles from the bizarre triangle-of-guns in Resonance of Fate, to the MMO cool-down combat of Xenoblade and the paradigm system in FFXIII.
I mean, by all means rail against the bad, recurring flaws of JRPGs (amnesiac teens, terrible anime characters and comedy animal/child party members killing special forces troops with ridiculous weapons like musical instruments etc are my bugbears), but you'd have to admit that the genre now encompasses so many styles and modern attempts to break from tradition that any attempt to describe the genre as only comprising those that look like JRPGs from the 90s just doesn't work any more.
Dragons Dogma is another wierd hybrid. Beautiful action-based combat, but there isn't any significant choice in the dialogue, and it feels just as much a JRPG because of Capcom's fluid combat taken from their action games as it does a western one for the quasi-photo-realistic art style. It's almost the opposite in that of Dark Souls, where the monsters have that wierd Japanese flair for the bizarre.
I just kinda think all RPGs exist on a bell curve at the moment, pigeonholing as 'western' or 'Japanese' as if those descriptives mean anything when considering hundreds of titles does a disservice to the games where developers have gone out of their way to escape the traditions of a genre and make something new.
I think JRPG kinda works as a descriptive of the 90s games like Chrono Trigger, Suikoden etc, where they all shared a lot of similarities. But these days there's so many different ideas that trying to decide whether each one still fits in that box is futile.