Two theaters. Sinbad and Toon. Poseidon is a full-on attraction that can’t really be converted into anything that different than what is already there. It may feature a performer, but it has more in common with Jungle Cruise than Borne. And what it does have in common with Borne, is that it’s mostly a movie. That isn’t exactly an easy or cheap thing to transition.
Sinbad was built specifically for a stunt show, including pretty elaborate set-pieces. That means they have to create a new stunt show with the same stunts, pay to convert the space to new stunts, or write a show that underuses the space completely.
Then there is Toon, which is arguably the best theater space on property. It can be rigged for flying stunts above the audience, it has a full fly system to change backdrops, and it’s just BIG. Its lack of use for guests is one of the biggest shortcomings at the entire resort.
So, why don’t they do anything with it?
For starters, it’s in an odd place. A Toon Lagoon show has already failed and the characters associated with land have lost the necessary relevance to make it a worthwhile draw. Only Peabody and Sherman have something current, but it’s not really popular. They could go with a Marvel show, but there’s a lot of risks if it’s a BAD show. They could go with something that loosely fits with Toon by strictly be animated, but then... well...
... where will the cheerleaders go?
Universal actually PROFITS off the theater being empty. The cheerleading competitions pay to use the theater, and Universal benefits from thousands of cheerleaders and their families going through the park to perform “at” Islands of Adventure.