Hi, I think the reason for this to catch players off guard. As you're well aware, the Battle Tree keeps getting tougher and tougher , and the AI better and better. It uses all sorts of tricks ranging from specific Pokemon to counter your specific team/sets to extreme RNG to downright dirty tactics (Minimize Toxic Protect Chansey, anyone?) to make you lose your streak.
Now think about this, if there's one superior set to Alakazam like your example, of course you'd prepare to counter that set. But if it's the other set, despite being objectively worse, it still catches you off guard. Imagine finally getting your +6 Dragon/Quiver Dances or Double Teams, and the opposing Alakazam suddenly uses Psych Up! Now all of a sudden an easy victory becomes a counter sweep, or a long drawn out PP Stall lasting hundred+ moves. The AI wants you to bungle up and lose, so it has multiple sets for the same Pokemon. That way, you never really which set you're up against.
I'm pretty sure the developers know that eventually the game will be data mined and all possible Pokemon will be listed out to help trainers maximize their chances of getting that 1000 streak. So, maybe their way of making it more challenging is to include some ridiculous sets that could break your run.
Another idea is that the sets are randomly generated for each Pokemon (not for each match) but while being coded, rather than spent potentially tens/hundreds of hours handpicking the best sets, some lazy/smart dev might automate the process using algorithms that could spew garbage sets or absolutely brilliant ones. That's of course, purely a guess from my end, I'm pretty sure GameFreak has many, many people working hard to make sure everything is perfect, but in today's age of algorithms, it just seems like another possible theory.
That, and as Polteageist mentioned, it could be for the memes. For game such as this, I bet there are nerd devs who giggle at dumb sets they included just because.
