By your reasoning the entire Death Star Trench sequence makes no sense-- why doesn't Darth Vader just force-wish all the Rebel fighters into the sides of the trench? Answer: because that ain't how it works.
If the Harryhausen homage of the arena sequence doesn't give you a thrill, then I'm sorry. But that's the reason it's there-- it's the kind of scene Lucas loves from the movies that inspired Star Wars and it's done to his taste here. I'm not thrilled with the beats of it and I look forward to the new version (where Anakin and Padme have a plan)-- but I sure get why it's there.
Did they really put these arena creatures into Happy Meals, or are you making that up?