Taming Sharks
If you want to get technical about it, you shouldn’t be able to tame jellyfish either. They don’t really have brains, and all they do is drift around waiting for food to run into them. They can’t keep up with your active swimming speed, let alone follow your commands in battle.
I just tell myself “this isn’t Earth.” Sure, that shark might LOOK like a tiger shark, but who knows how the ecology of this planet works? Sharks in the game’s universe are able to be tamed and follow your commands.
Though I agree, you should have the option to tame dolphins as well.