there are several reasons.

- Fire hazard: A space as large as these big box floor areas have to be divided into smaller fire skirts on the ceiling to contain the spread of a potential fire. If you look up to the ceiling you will see it is being partitioned by either corrugated sheets or some other noncombustible material hanging from the ceiling into a square pattern of parapets.

- Storage space of the merchandise stacked up and enough height for the lift trucks to easily move them up and down. The storage is right above the merchandise.

- Architectural considerations. A short very large space ceiling is not flattering at all, would not have a pleasant scale, and look welcoming, worse when it is cluttered with suspended signs.

- Acoustics, It will be Reflect and amplify the noises.