(Edit, 21:04 EDT: Fixed the link. For whatever reason I linked to the wrong thing. Sorry about that.)
Because of course it was going to happen eventually. Right now there's an ongoing competition for the otherwise unavailable Charizardite Y, and only the top scorers in each region will get it (although there are other prizes up for grabs). Unfortunately, the game's programming appears to be anything but foolproof, as malicious individuals gained the ability to use unreleased Pokémon to dominate the rankings, and possibly screw legit players out of their Charizardite Y. The chief offender here is, of course, Ditto - while I don't think it's ever going to be intended as an actual support Pokémon, it's still in the game code for whatever reason. I'm assuming it's meant to be a feature in yet-to-be-released stages. Anyway, if you're familiar with Trozei, you know what this does - it's essentially a wild card, being able to match with anything. And what happens when a quarter of the Pokémon on the board are wild cards (provided you use a Complexity -1 to get rid of Fennekin)? Of course the end result is neverending combos, and the results obtained are nothing short of outrageous. While the current top legit players, invariably using the same ol' Mega Gengar + Arceus + two out of Snorlax, Lickilicky and Blissey, scramble to top the magical 100k mark (the current leader in North America is sitting at 99916), some cheaters managed to get as high as 660k by using not only Ditto, but also Palkia, an unreleased Pokémon that provides extra power over Pokémon that are currently available (since there are only two super-effective Pokémon with 80 base power to go along with Ditto, whereas three are required).
It's safe to assume that those competitions are where Genius Sonority is making a mint. Ranking high enough to get a Mega Stone without buying every item available is nothing short of unthinkable, and those items are expensive and add up very quickly. For that reason, many people opt to do only one attempt with all items and pray to Arceus they'll rank high enough. But not everyone does that, and the lure of powerful mega evolutions, especially those like Garchomp, Lucario or Charizard that have typings without a mega in the base game, will be enough to get people to fork over some cash to buy in-game money and do more than one attempt. And don't quote me on that, but I'm pretty sure that guy that has 99916 points didn't do it in one try.
As a result, hacking deprives them of a lot of revenue - that potentially paid by the hackers themselves, since they can just get their Charizardite Y on their own (so basically they're just assholes who want to prevent someone out there from getting theirs), and that paid by the legit players, who see this and wonder, what's the point, you need to hack to get the stone anyway.
And one of the few perks of a game with microtransactions is that there's added incentive to preserve the integrity of the game, otherwise the cash cow dries up. Fortunately, Genius Sonority is aware of those recent developments, as they've banned those people who were dumb enough to use Ditto and Palkia. People like this guy. (Man, just seeing this makes me so happy in my pants.) Those who hacked to get Arceus, on the other hand, are probably not going to get the banhammer, since it IS legitimately attainable... it's just that it's a previous event, and a difficult one at that, so some people may not have it.
Now here's hoping that they beef up their security a bit before doing more competitions. We don't need this to happen every time one of those happens.