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The fact that you can only get Dive Balls in gen IV from doing the newspaper requests. They didn't bring them back to be sold normally in BDSP either. There's a new item seller in Ramanas Park that sells every other type but not Dive. At least back in gen IV they were still programmed to only be effective underwater so they probably thought it seemed pointless, but in recent gens they work better against any mon found surfing or fishing too.
And on a related note, the artificial scarcity of apricorn balls. I just want to use them regularly and not have to save them for when something really piques my balltism and then reset when it busts out because you only get one or two a game now. And yeah I know lorewise they're rare because only Kurt makes them but you can handwave that with a line about Kurt teaching apprentices his techniques or selling them to a corporation. Or ignore it altogether, who gives a fuck. Game Freak only cares about lore when it suits them anyways.