LOL, I know, right? See, I'd be irritated too if it wasn't for the fact that the Keyblade is pretty much the weapon that EVERYBODY USES NOW. Sure, Donald and Goofy fight without one, and Axel fights without one, but how many other main, main characters don't wield one? Plus, I just think it wouldn't look good if they chose to make SRK the next TAV and Kairi didn't have a Keyblade. Or if they even centered the entire story on the destinies of Sora, Riku, and Kairi...and Kairi was the only one in the group without a Keyblade. Plus, it ends up looking sexist too, if Aqua is the only girl out of MANY males who can wield. Unintentional sexism, probably, but try telling that to feminists who are already on Disney's case about their princess characters.
And on that note, I do understand the frustration about the Princesses because I really love those characters and I wanted to see more of them. But if Nomura's not going to do anything with them, then I'm satisfied with him turning Kairi into a wielder. And as I keep saying, who says that's the end to her role as a PoH? She could always, you know, use the Keyblade to channel those powers. Nor do I think it was badly explained. If anything SORA getting a Keyblade turned out to be more of a fluke than KAIRI because Sora never underwent the Rite of Succession. Kairi and Riku did, even if Kairi's wasn't intentional. *sigh* KH3, where are you???