Well a lot of people clearly don't see it that way considering all the sequels and spin offs that have been justified to be funded and produced and obviously many people buy it outside Japan. Personally, I think KH is one of my favourite series, if not my most, and I think one reason is that the game surprised me. When I was a kid, browsing in a game shop one day with my parents, my mum looked at this game, "Ohh, this looks good", I looked at it, I see a heart-moon on the box, and donald/goofy on it, "Nah, it's gonna be a kiddy game", we left it. Then another day in the future, mum bought it for me anyway, so gave it a try at least, as to not be a dick, and I ended up loving it ever since. The story was just not was I was expecting at all, it was a challenging game, and I didn't find the game "overly" kiddy at least, I guess it's more seeing the disney worlds in the eyes of someone who hasnt experienced them before, yet it's all possibly familiar to you. At least most of it was to me. While the story is "convulted" as some say and even I, don't think I would go through the ordeal of explaining all of it to someone, I do still enjoy it, I want to know how this all ends, and I think it's the plot that really ties the whole game together, disney+FF, without it, I don't think it would have worked nearly as well.
Just pretty harsh to say most of what you say as if it's a fact to everyone, only thing you can say that's a "fact to yourself" is your opinion of the game, you can't really claim to know how others see the game.