The concept of an automated parking garage is highly attractive to developers who want more efficient use of space. Since land is expensive, they want to optimize every square inch. It’s hard to do this when you need to consider pedestrian traffic, ramps, turn radius, door openings, stairs, toilets, guard stations, and so on.
If automation is employed, then these will no longer influence the design. The slots can have lower ceilings and narrower widths. After all, passengers will leave the car at the entrance and let the system move the vehicle to its designated space. The belts have precise movements. They are unlikely to commit errors as long as the system is well-maintained.
Smaller slots mean more cars can fit per level. More cars mean more paying customers for the parking garage. It will be easier to recover the cost of the development and make the business profitable.