>>51570077Leon said Eternatus hadn't yet learned how to fully control its power. It would be a bad look for the world champion if he unleashed a potentially dangerous Pokemon in a packed stadium because of how utterly reckless it would be.
I think this was just the anime's way of concluding Eternatus' story, if you could even call it that, and possibly further boost Leon's status as trainer ahead of the finals. Make him seem even more impressive, y'know, since he's made progress taming what was (and still could be) a dangerous Pokemon.
