I think the key thing is that the Pokemon games tend to have better pacing, especially in their early game. While there is some necessary tutorialising in most Pokemon games you are out of the starting town with your starter Pokemon and are catching additional Pokemon within 30mins or so. While more traditional JRPGs (particularly older ones) tend do keep you in the default starting town for quite a while until the inciting incident happens. For example if Pokemon Red/Blue were a more standard JRPG you'd start the game in your home town and having to faff about there for an hour or two before moving to Pallet Town which would function as the inciting incident and the thing that would thrust you on your journey. I also think the Pokemon games' light touch to giving detail to the setting and characters (with a few exceptions) really allows the player to project themselves and their viewpoint on the world. It you on the journey rather than you assuming the role of a plucky hero with funny hair.