The Jarlsen-Barteltran is an old theatre. The balconies predate the development of the Theatre Orb by quite some time. It's not that there was a redundant balcony constructed just for that purpose, it's more that the original designers didn't think the layout through that well, resulting in one balcony with a significantly worse view of the stage for the theatregoers.

Early applications of the Theatre Orb were handled backstage, where it was quickly discovered that the operator needs a better view of the stage in order to properly deploy the effects. While that balcony was bad for paying customers, they found that it offered a good enough view of the stage to manage effects, and as Alex correctly stated, they weren't losing any business from a seat nobody wanted anyway.