It's a competition with VGC rules. And as the first VGC year of the latest generation, Pokemon not in the Alola Pokedex are not allowed.The new rules for the April Competition.
The fact that unless you've beaten the game, have the necessary items (or can get them quickly enough), and the means to raise Pokémon in the necessary time, there is zero point in entering the April competition.
I haven't completed Sun, and am not in a position to beat the game anytime soon, so bred by Pokémon in Alpha Sapphire, since I was able to use Pokémon brought over from there in the last competition. So when I found out that you can only use Pokémon you've raised in Sun, I was absolutely outraged. I mean, hello! Not everyone has beaten the game! They can't spend hours upon hours doing so! If I tried, I wouldn't hear the end of it from my parents, and rightfully so. I'm not some kid who can afford to spend all of his free time playing on his Gameboy!
All that time breeding and raising a team was a waste, and even then, it would have been a challenge, due to not having access to the Beasts and Tapus. But this is the last straw. Unless someone is willing to breed and raise my entire team (I can't even do the latter), there is zero point in entering, because what I caught in Sun is shit compared to what I'd have to got up against. I would loose every battle.
The Mega Stones had better be released again at a later time, or I will give Nintendo of America a piece of my mind. What's the point of entering a competition if you can't even hope to win a single fucking battle?
It's been this way since VGC '11 at latest, nothing new.
And besides, it's april. Almost half a year has passed since the games were released.