Suburban buildings can be bigger - and can more easily meet the standardized requirements of national merchandisers. The bigger a new building, the lower its square-foot costs for leasing. In smaller, downtown spaces, economies of scale are hard to obtain, and zoning may limit building heights. Also, corporate retailers tend to seek prototype rectangles with ample floor space. These are easier to provide on new, spacious suburban sites.
Parking is ample.
The more sprawled in size a suburban lot is, the more parking area it is likely to provide.